Prothrombin Time Testing Practices in the Pacific Northwest:
A Model for Monitoring Voluntary Practice Guidelines
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Survey Home
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Findings
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Purposes for performing PT testing
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Participants were asked if they performed PT for any of the following purposes:
-
evaluation of bleeding,
-
detection of factor deficiencies,
-
assessment of liver disease,
-
monitoring of oral anticoagulation therapy, and
-
other.
Of the 297 respondents, 263 (89%) stated that they performed PT for at least
one of the 4 indications, with one respondent performing PT (for evaluation of
bleeding and detection of factor deficiencies) but not monitoring oral
anticoagulation therapy. There were 5 respondents (2%) who did not note
whether they performed PT assay for any of the 4 specific reasons above. Of the
respondents, 28 (9%) noted that they did not perform PT for any of the above
4 indications and 1 (0.3%) stated not monitoring for oral anticoagulant therapy
without answering if they performed PT for any of the other 3 specific
indications.
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Table 3 - Purposes for performing PT testing
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Purpose
|
Proportion* (Number)
|
| Monitoring of oral anticoagulation therapy
|
99.6% (262) |
| Evaluation of bleeding |
84% (205) |
| Assessment of liver disease |
76% (177) |
| Detection of factor deficiencies |
67% (153) |
| Other responses were pre-surgical testing, deep vein thrombosis,
chest pain, baseline for cardiac profile, lupus anticoagulant testing, and
whatever the doctor wanted. |
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*Proportions of affirmative responses after exclusion of those not
responding affirmatively to at least one of the 4 specific indications noted
for PT testing.
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Since the focus of this questionnaire was the use of PT testing to monitor oral
anticoagulation therapy, only participants responding affirmatively to such a
use were asked to complete the remainder of the questionnaire.
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Performing PT testing in more than one location
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Given a list of choices, participants were asked if PT testing was performed in
more than one location in their facility. Seventy-seven of 262 respondents
(29%) answered "Yes" to this question.
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Table 4 - Other Locations where PT testing is performed (N = 77*)
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Location
|
Number (Proportion*)
|
| Anticoagulation clinic
|
39 (51%) |
| Patient draw station |
18 (23%) |
| Patient exam room |
13 (17%) |
| Nursing station |
10 (13%) |
| Other responses (N = 28, 36%) were endoscopy department, patient
bedside, chemotherapy room, home health, emergency department, satellite
laboratory, core laboratory, outpatient clinic, hospital in another city, and
home. |
|
*The denominator used for proportions was the number of respondents
(N = 77) checking at least 1 of the 4 choices. There was a respondent who had
not checked any choices but had noted a testing site other than the central
laboratory in the section labeled other. This respondent was included in the
denominator.
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Participants were asked to answer the remaining questions for the method they
performed and not for testing done in any other location in their facility.
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Patient self-testing devices
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Of 259 respondents, 13 (5%) were aware of PT testing being performed by their
patients on a self-testing device.
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Thromboplastin reagents used
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Two hundred and fifty-one respondents gave a manufacturer and/or brand name of
the thromboplastin reagent used. One hundred seventy six (70%) indicated they
used a reagent associated with a traditional PT test method and 75 (30%)
noted the use of reagent test strips or cartridges associated with POC testing
devices. Table 5 shows the demographics of sites according to these 2 different
types of methods.
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| Table 5 - PT test methods (N = 251 sites) |
|
Percent of Sites (N) |
|
Hospital |
IL |
POL |
| Traditional methods |
61 (108) |
13 (22) |
26 (46) |
| POC devices |
6 (5) |
1 (1) |
92 (69) |
|
|
Traditional methods
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Sensitivity of PT assay to heparin. According to consensus guidelines
developed at the 1997 CAP conference on laboratory monitoring of oral
anticoagulation therapy, users should determine the sensitivity of their PT
assay to heparin and, where possible, select a reagent that is insensitive to
heparin in the therapeutic range (3). Therefore, participants were asked if
they determined the sensitivity of their PT assay to heparin and if they
selected a reagent that is insensitive to heparin in the heparin therapeutic
range. In patients where rapid anticoagulation is required, heparin may be used
initially and overlapped with warfarin for several days. Many thromboplastin
reagent package inserts give an indication of the sensitivity of their reagent
to heparin.
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Of the respondents using traditional methods, 15% (26/169) determined the
sensitivity of their assay to heparin and 54% (83/154) stated they selected a
reagent that was insensitive to heparin in the therapeutic range. This is
primarily an important feature for hospitalized patients and we found that
20% (22/112) of the hospital respondents determined the sensitivity, 58%
(62/107) selected an insensitive reagent, and 64% (69/108) did one or the
other to alleviate this concern about heparin interference with PT assays.
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ISI values. When using the PT test to monitor oral anticoagulation
therapy, the sensitivity of the thromboplastin reagent to the depletion of
vitamin K dependent coagulation factors is reflected as the international
sensitivity index (ISI). All thromboplastins are calibrated against standards
with sensitivities comparable to the WHO international reference plasma, which
is assigned an ISI of 1. Commercial manufacturers of thromboplastin reagents
calculate the ISI and include it in the product package insert.
|
Several voluntary practice standards and other publications recommend the use
of thromboplastin reagents that have a low ISI value (3-7). Thromboplastins
with low ISIs are more responsive or "sensitive." The variability of INR values
produced by different test systems may be reduced by the universal use of
highly responsive reagents.
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|
While sensitive thromboplastin reagents with lower ISI values may offer the
potential for improved precision in determining the INR [due to the fact that
INR = (PT ratio)ISI where PT ratio = patient PT/mean normal PT],
some studies have suggested that low-ISI reagents may be less precise (6). The
following recommendations have been made for the selection of reagent ISI
values:
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| 0.90-1.70
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|
CAP (3) |
| <1.51 |
|
CLSI (4) |
| Close to 1.00
|
|
American Society of Health System Pharmacists (5) |
| <1.21
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|
Hirsch (6) |
| <1.51 |
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American Heart Association (7) |
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Table 6 shows the ISI ranges of the reagents used for PT assay.
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Table 6 - PT reagents - Traditional methods (N = 176 sites)
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| Reagent manufacturer |
Number of respondents |
Examples of brand names |
Range of ISI values* |
| Dade Behring |
58 |
Innovin
Thromborel S
|
0.90-1.13 |
| Thromboplastin C+ |
1.77-2.21 |
| Beckman Coulter/ Instrumentation Laboratory |
50 |
IL PT-Fibrinogen Recombinant
IL PT-Fibrinogen HS+
|
0.85-1.13 |
| IL PT-Fibrinogen HS |
1.35-1.44 |
IL PT-Fibrinogen
IL Thromboplastin |
2.00-2.23 |
| BioMerieux |
24 |
HTF |
1.15-1.26 |
| Simplastin Excel |
1.81-1.91 |
| Diagnostica Stago |
13 |
Neoplastin
Neoplastin C1+ |
1.26-1.35 |
| Hemoliance |
11 |
Recombiplastin RTF |
0.94-1.03 |
| Brain thromboplastin |
2.00-2.33 |
Sigma Diagnostics/
Sigma Trinity Biotech |
10 |
Thrombomax HS
Thromborel HS |
1.15-1.31 |
| Thrombomax |
1.69-1.71 |
| Pacific Hemostasis |
6 |
|
1.16-2.04 |
| Ortho
|
3 |
None given |
0.85 to 1.00 |
| Other
|
1 |
MLA Recombiplastin |
1.03 |
| Total |
172 |
|
0.85-2.33 |
|
*There were 4 respondents who noted the name of their reagent
manufacturer without providing their reagent's ISI.
|
For sites using traditional methods, the range of ISI values for their reagents
was 0.85 to 2.33, with an average ISI of 1.34 and median ISI of 1.15 (N = 172).
Table 7 shows a frequency distribution of the reagents used according to ISI
values.
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Table 7 - Distribution of reagents by ISI values (N = 172 sites)
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ISI Values
|
Number (Proportion)
|
|
< 1.20
|
91 (53%)
|
|
1.20-1.49
|
36 (21%)
|
|
1.50-1.69
|
3 (2%)
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|
1.70-1.99
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20 (12%)
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|
2.00-2.40
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22 (13 %)
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When asked if they used a voluntary practice standard to guide them in the
selection of their reagent, 25% (43/174) using traditional methods responded
"Yes," and 21% (36/174) gave the name of a voluntary practice standard or
guideline. The following summarizes these responses:
|
| Voluntary practice standard
|
Number of sites |
| CLSI |
29 |
| CAP |
12 |
| WHO |
5 |
| Chest |
2 |
| Archives of Pathology & Laboratory Medicine |
2 |
| American Society of Thrombosis & Hemostasis |
1 |
| |
| Other sources mentioned |
|
| Manufacturer's recommendations |
4 |
| Corporate standards |
2 |
| COLA |
2 |
| Code of Federal Regulations (CFR) |
1 |
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The majority of the respondents noted that they either did not use voluntary
practice standards or were not aware of them. Of the respondents using
traditional methods, 38% (66/174) responded "No" and 37% (65/174) responded
"Do not know." The reasons given by sites that did not use a standard are
summarized as follows:
|
|
Reason
|
Number of sites*
|
| Not aware of practice standards addressing this |
32 |
| Performed our own studies |
20 |
| Performed our own literature review |
17 |
| Recommended by manufacturer for our instrument |
8 |
| Cannot afford to purchase practice standards |
7 |
| Reagent selected to match/correlate with another lab |
2 |
| Reagent selected by corporate or parent lab |
2 |
| Do not agree with the standard |
1 |
| Reagent is common in our area |
1 |
| We are part of a buying group |
1 |
|
*Based on the response patterns to this question, and others
questioning why respondents did not use a voluntary practice standard, we chose
to reflect only affirmative responses as numbers in rank order. Those
responding that they were not aware of practice standards tended to not answer
any subsequent questions. We considered 1 response pattern to be contradictory:
not being aware of practice standards while not agreeing with the standard. In
such a case, both affirmative responses were excluded. One respondent was
excluded due to such an inconsistent response pattern.
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Point of care devices
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Of the respondents using POC devices, 3% (2/66) determined the sensitivity of
their POC reagents to heparin and 14% (8/58) stated they selected a reagent
that was insensitive to heparin in the therapeutic range. Of the 5 hospitals
performing POC methods, none determined the sensitivity of the PT assay to
heparin and only 1 s tated selecting a reagent that was insensitive to heparin
in the heparin therapeutic range. The following table summarizes the POC
devices used by the respondents:
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Table 8 - PT reagents - POC devices (N = 75 sites)
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Manufacturer
|
Examples of Brand names
|
Number of Respondents
|
ISI values
|
| Roche Diagnostics |
CoaguChek
CoaguChek S |
61 |
2.00 (29 sites)
1.00 ( 2 sites)
No value given (30 sites) |
International
Technidyne
Corporation |
Hemochron Jr
Protime
Protime 3 |
8 |
1.00 |
| Bayer Diagnostics |
PT-NC
RapidPoint
Thrombocard |
5 |
1.00-1.20 |
| Hemosense |
INRatio |
1 |
1.00 |
|
|
When asked if they used a voluntary practice standard to guide in their
selection of their PT reagent, 11% (7/65) of the respondents using POC devices
said "Yes" and 11% (7/65) named a standard. The following summarizes their
responses:
|
| Voluntary practice standard |
Number of sites |
| CAP |
2 |
| CLSI |
1 |
| Other sources mentioned* |
| Manufacturer's recommendations |
2 |
| JAMA, American Journal of Clinical Pathology, and CAP |
1 |
| COLA |
2 |
*There were 2 respondents noting CLIA as other sources even though
CLIA is known to be regulatory and not a voluntary practice standard.
|
|
Of the respondents using POC devices, 45% (29/65) responded "No" and 45%
(29/65) responded "Do not know." The reasons given by sites that did not use a
standard are summarized as follows:
|
| Reason |
Number of sites |
| Not aware of practice standards addressing this |
17 |
| Standards do not apply to my method |
9 |
| Performed our own literature review |
3 |
| Performed our own studies |
3 |
| Reagent is matched to our instrument |
2 |
| Test system is POC device, finger stick method |
2 |
| Cannot afford to purchase practice standards |
1 |
| ISI and calibrations set at factory, predetermined |
1 |
| Do not use reagent |
1 |
| Follow manufacturer guideline |
1 |
|
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Testing personnel
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Given a list of personnel training backgrounds, participants were asked to list
the numbers of each type of personnel that performed PT testing. A wide variety
of backgrounds of testing personnel were given. Different patterns were seen in
testing personnel between the sites using traditional test methods and those
using POC devices.
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|
Traditional methods
|
There was an average of 10 testing personnel per site, with a range of 1 to
70 per site (median, 6; N = 158). Ten different training/experience backgrounds
were given. Of the 174 sites answering this question, 173 (99%) employed at
least one medical technologist or medical laboratory technician as testing
personnel.
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Table 9 - Testing personnel performing traditional methods (N = 174 sites)
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| Testing personnel background |
Sites employing testing personnel with the background |
| |
Number |
Percent |
| Medical technologist |
171 |
98 |
| Medical laboratory technician |
99 |
57 |
| On the job trained |
9 |
5 |
| Pharmacist |
3 |
2 |
| Registered nurse |
3 |
2 |
| Laboratory assistant |
3 |
2 |
| Phlebotomist |
3 |
2 |
| Non-registered tech |
2 |
1 |
| Medical assistant |
2 |
1 |
| Advanced registered nurse practitioner |
1 |
0.6 |
|
|
Point of care devices
|
There was an average of 6 testing personnel per site, with a range of 1 to
100 per site (median, 4; N = 64). Twelve different training/experience
backgrounds were given. Of the 74 sites answering this question, 46 (62%)
employed at least one medical technologist or medical laboratory technician as
testing personnel.
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Table 10 - Testing personnel using POC devices (N = 84 sites)
|
| Testing personnel background |
Sites employing testing personnel with the background |
| |
Number |
Percent |
| Medical technologist |
34 |
46 |
| Medical assistant |
33 |
45 |
| Medical laboratory technician |
27 |
36 |
| Registered nurse |
23 |
31 |
| On the job trained |
13 |
18 |
| Licensed practical nurse |
12 |
16 |
| Pharmacist |
4 |
5 |
| Phlebotomist |
4 |
5 |
| Physician assistant |
3 |
4 |
| Laboratory assistant |
2 |
3 |
| Emergency medical technician |
1 |
1 |
| Advanced registered nurse practitioner |
1 |
1 |
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Specimen collection and handling
|
Participants were asked if they collected samples for PT by venipuncture. Of
the 260 respondents to this question, 216 (83%) indicated they did.
Sodium citrate concentration. Several voluntary practice standards or
guidelines recommend the use of collection tubes containing sodium citrate in
the concentration of 3.2% (3, 8-10). The INR can be affected by the citrate
concentration. Many of the manufacturers determine their ISI values using 3.2%
citrate; therefore, the same citrate concentration should be used in individual
laboratories. Low ISI reagents yield higher INR values when under-filled
samples are collected in 3.8% citrate (11).
Of the 206 sites answering this question, 190 (92%) used only the recommended
citrate concentration of 3.2% . The following table summarizes the responses.
|
|
Table 11 - Citrate concentration of specimen collection tubes (N = 206 sites)
|
|
Sodium citrate concentration
|
Number of respondents
|
Percent
|
| 3.2% |
190 |
92 |
| 3.8% |
8 |
4 |
| 3.2 % and 3.8% |
2 |
1 |
| Do not know concentration |
1 |
0.5 |
| Did not choose a concentration |
5 |
2 |
|
When asked if they used a practice standard to guide their selection of citrate
concentration of the collection tubes used, 39% (82/209) stated "Yes," and
34% (69/205) named a voluntary practice standard. The following summarizes
their responses:
|
| Voluntary practice standard |
Number of sites |
| CLSI |
63 |
| CAP |
24 |
| WHO |
5 |
| International Society of Thrombosis & Hemostasis (ISTH) |
1 |
| American Society for Clinical Pathology (ASCP) |
1 |
|
Other sources mentioned
|
| Manufacturer recommendations |
5 |
| Selected by corporation |
2 |
| Selected by local laboratory |
1 |
|
*There was 1 respondent noting CLIA and Washington State regulations
as other sources even though they are regulatory and not voluntary practice
standards.
|
|
Sixty-four of the 209 respondents (31%) stated "No" and 63 (30%) responded
"Do not know." The reasons given by sites not using a standard are summarized
as follows:
|
| Reason |
Number of sites* |
| Not aware of practice standard addressing this |
32 |
| Performed our own literature review |
20 |
| Performed our own studies |
15 |
| Cannot afford to purchase practice standards |
6 |
| Follow manufacturer's recommendations |
6 |
| To correlate with another laboratory |
5 |
| Standards do not apply to my method |
3 |
| Collection tubes already in place before I started |
2 |
| Corporate decision |
2 |
| A reference lab supplies us / Wish to standardize with reference lab |
2 |
| Advised by hospital |
1 |
|
*We considered 1 response pattern to be contradictory: not being
aware of practice standards while not agreeing with the standard. In such a
case, both affirmative responses were excluded. One respondent was excluded due
to such an inconsistent response pattern.
|
Specimen rejection criteria. Of the 216 respondents that collected
samples by venipuncture, 202 (94%) said they had a written policy addressing
specimen acceptability and rejection for PT testing.
|
There are many voluntary practice standards that address the proper collection
of specimens for coagulation testing and PT testing in particular (4, 8, 12).
|
When asked if they used a practice standard to develop their specimen
collection policies, 46% (94/205) of respondents said they did, and 37%
(75/205) named a voluntary practice standard. The following summarizes their
responses:
|
| Voluntary practice standard |
Number of sites |
| CLSI |
67 |
| CAP |
17 |
| WHO |
5 |
| ASCP |
2 |
| ISTH |
1 |
| Other sources mentioned* |
| Manufacturer recommendations |
16 |
| Literature study, reference books |
4 |
| COLA |
2 |
| CLIA |
2 |
| Corporate decision |
1 |
|
*There were 2 respondents noting CLIA as other sources even though
CLIA is known to be regulatory and not a voluntary practice standard.
|
|
Fifty-two of 201 respondents (26%) responded "No" and 55 (27%) responded
"Do not know." The reasons given by those who did not use a standard are
summarized as follows:
|
| Reason |
Number of Sites* |
| Not aware of practice standard addressing this |
28 |
| Performed our own studies |
15 |
| Performed our own literature review |
13 |
| Cannot afford to purchase practice standards |
5 |
| Standards do not apply to my method |
3 |
| Follow manufacturer's recommendations |
3 |
| Used a policy from where I worked before |
1 |
|
*We considered 1 response pattern to be contradictory: not being
aware of practice standards while not agreeing with the standard. In such a
case, both affirmative responses were excluded. One respondent was excluded due
to such an inconsistent response pattern.
|
Participants were given a list of issues that are commonly recommended for
inclusion in specimen acceptability and rejection policies for coagulation
testing. They were asked to acknowledge those they included in their written
policy.
|
|
Table 12 - Specimen acceptance and rejection policies
|
| Specimen acceptance/rejection issue |
Proportion (Number)* |
| Properly anticoagulated specimen |
97% (194) |
| Correct volume of blood |
97% (194) |
| Appropriate storage temperature |
97% (189) |
| Time delays prior to testing |
96% (187) |
| Adequate labeling of specimen |
96% (190) |
| Adequate centrifugation (speed and time) |
92% (178) |
| Information on requisition and specimen label match |
90% (174) |
| Adequate information on requisition |
90% (173) |
| Hemolysis |
89% (170) |
| Appropriate transport times |
89% (168) |
| Order of multiple tubes |
86% (166) |
| Lipemia |
78% (146) |
| Drawing specimens from patient lines |
73% (136) |
| Icterus |
71% (131) |
| Difficult draws |
67% (127) |
| Collection of samples in a syringe |
66% (129) |
| Abnormal hematocrits |
65% (123) |
| Heparinized specimens |
60% (113) |
|
* Number refers to those responding affirmatively to each question
and proportions are the percent affirmative responses of all responding either
affirmatively or negatively to each question. There was 1 respondent noting
that they had a written specimen acceptance/rejection policy for presence of
lupus anticoagulant.
|
It should be noted that depending on the setting or the methodology, some of
specimen rejection criteria may not apply. For example, the collection of
samples from patient lines and heparinized specimens may be applicable for
patients in hospitals, but not for most patients in outpatient settings.
Specimens that are icteric or lipemic may affect test methods based on optical
clot detection, but may not be a concern for mechanical clot detection
methodologies.
|
Of the 259 respondents, 85 (33%) stated that they collected samples by finger
stick or capillary collection. Of the 82 respondents, all collecting capillary
samples, 71 (87%) indicated that they had a written policy addressing the
proper collection of capillary specimens for PT testing.
|
|
Checking out new lots of reagents
|
Various practice standards address issues associated with implementing new lots
of testing reagents. Some address general activities such as establishing or
verifying patient reference ranges and mean of normal, and some are specific
for handling new lots of thromboplastin reagents (3-5, 12, 13).
|
Given a list of 8 indicators of quality practices associated with checking out
new lots of thromboplastin reagents for PT testing, participants were asked
which ones they performed.
|
Traditional methods
|
|
Table 13 - Checking out new lots of reagents - Traditional methods
|
|
Quality Practice
|
Proportion (Number) * |
| Establish patient mean of normal |
95%(158) |
| Conduct parallel testing between lots |
93% (156) |
| Verify reference (normal) range |
92% (153) |
| Confirm calculations of INR |
89% (148) |
| Verify that the ISI is correct for instrument/reagent combination |
89% (147) |
| Alert clinicians when new reagent or reagent with different ISI placed in use |
66% (107) |
| Perform correlation studies with another method or site |
42% (67) |
| Establish ISI with calibrators |
20% (32) |
|
*Number refers to those responding affirmatively to each question
and proportions are the percent affirmative responses of all responding either
affirmatively or negatively to each question.
|
When asked if they used a practice standard to develop their policy for
checking out new lots of reagents, 37% (63/172) said they did, and 32%
(55/172) named a voluntary practice standard. The following summarizes their
responses:
|
| Voluntary practice standard |
Number of sites |
| CLSI |
44 |
| CAP |
23 |
| WHO |
1 |
| ASCP |
1 |
| ISTH |
1 |
| Other sources mentioned* |
Number of sites |
| Manufacturer recommendations |
10 |
| Performed our own studies |
2 |
| Follow corporate policy |
1 |
|
*There were 2 respondents noting CLIA as other sources even though CLIA is known
to be regulatory and not a voluntary practice standard.
|
Fifty-nine of the 172 sites (34%) responded "No" and 50 (29%) responded "Do
not know." The reasons given by those not using a standard are summarized as
follows:
|
| Reason |
Number of sites* |
| Not aware of practice standard addressing this |
36 |
| Performed our own studies |
21 |
| Performed our own literature review |
12 |
| Cannot afford to purchase practice standards |
5 |
| Follow manufacturer's recommendations |
4 |
| Follow CAP policy, CAP website |
2 |
| To correlate with hospital |
1 |
|
*We considered 1 response pattern to be contradictory: not being
aware of practice standards while not agreeing with the standard. In such a
case, both affirmative responses were excluded. One respondent was excluded due
to such an inconsistent response pattern.
|
Point of care devices
|
Table 14 lists selected practices followed by the respondents.
|
|
Table 14 - Checking out new lots of reagents - POC devices
|
| Quality practice |
Proportion (Number)* |
| Verify reference (normal) range |
62% (36) |
| Verify that the ISI is correct for instrument/reagent combination |
60% (35) |
| Perform correlation studies with another method or site |
40% (22) |
| Establish patient mean of normal |
35% (19) |
| Conduct parallel testing between lots |
35% (19) |
| Confirm calculations of INR |
34% (19) |
| Alert clinicians when new reagent or reagent with different ISI placed in use |
33% (19) |
| Establish ISI with calibrators |
30% (17) |
|
*Number refers to those responding affirmatively to each question
and proportions are the percent affirmative responses of all responding either
affirmatively or negatively to each question.
|
|
When asked if they used a practice standard to develop their policy for
checking out new lots of reagents, 25% (16/65) of the respondents said they
did, and 5% (3/65) named a standard. The following summarizes their responses:
|
| Voluntary practice standard
|
Number of sites |
| CLSI |
2 |
| CAP |
1 |
| Other sources mentioned |
Number of sites |
| Follow manufacturer recommendations |
8 |
| Test controls |
3 |
| COLA |
1 |
| Recommended by company |
1 |
Thirty of the 65 sites (46%) responded "No" and 19 (29%) responded "Do not
know." The reasons given by those not using a practice standard are summarized
as follows:
|
|
| Reason |
Number of sites |
| Not aware of practice standard addressing this
|
17 |
| Standards do not apply to my method |
9 |
| Performed our own literature review |
4 |
| Follow manufacturer's recommendations |
4 |
| Performed our own studies |
3 |
| Standards are too complicated |
1 |
| Method is waived; calibrated at the factory |
1 |
| Not aware needed for POC device |
1 |
| Use pre-packaged reagents |
1 |
| Cannot afford to purchase practice standards |
1 |
|
|
Patient test reports
|
The WHO, along with the ISTH, recommends that reporting of PT results for
patients on oral anticoagulation therapy include the use of INR values (10,
14). Other practice standards and publications suggest this as well (3, 4, 6,
12). Given a list of choices, participants were asked which test values and
other information they provide in the patient report to clinicians.
Table 15 lists the measurement units and results interpretations/comments
provided by the respondents.
|
|
Table 15 - Patient test reports
|
| Test value |
Proportion (Number)* |
| PT as INR |
99.6% (232) |
| PT in seconds |
89% (204) |
| PT ratio |
7% (14) |
|
Other responses were patient mean of normal value (N = 4), normal control value
(N = 2), QC (N = 1), therapeutic ranges (N = 1), and last dose of medication (N
= 1). In all these cases, PT was reported in both seconds and INR.
|
|
Interpretation or comments
|
| Reference (normal) ranges |
84% (211) |
| Specimen comments |
79% (195) |
| Therapeutic ranges |
74% (182) |
| Interpretation |
30% (66) |
|
Other responses were dose of medication (N = 5), clinician seeing patients and
knowing what ranges/interpretations are (N = 2), extenuating circumstances (N =
1), and normal patient mean (N = 1).
|
|
*Number refers to those responding affirmatively to each question
and proportions are the percent affirmative responses of all responding either
affirmatively or negatively to each question.
|
|
Repeating patient tests
|
To evaluate how personnel judge test result acceptability, we asked what
prompted them to repeat a patient test result, given a list of choices.
|
|
Table 16 - Reasons for repeating a patient test
|
| Reason |
Proportion (Number)* |
| Instrument failure or flag |
99% (255) |
| Quality control values outside of acceptable limits |
97% (243) |
| Critical patient value |
95% (244) |
| Unusual value for patient's history |
82% (204) |
| Abnormal patient value |
59% (148) |
| Information from patient interview |
34% (80) |
| Computer tracking system |
29% (69) |
|
Other responses were perform tests in duplicate (N = 2), if clinician requests
it (N = 2), doctor tracking results on patient chart (N = 1), invalid test
result (N = 1), and delta check (N = 1).
|
|
*Number refers to those responding affirmatively to each question
and proportions are the percent affirmative responses of all responding either
affirmatively or negatively to each question.
|
|
General quality assurance (QA) and competency assessment
activities
|
Given a list of 10 QA procedures, participants were asked which they performed.
The responses are summarized in the following table.
|
|
Table 17 - Quality assurance procedures
|
| Quality assurance procedure |
Proportion (Number)* |
| Immediately alert clinician about critical test results |
100% (254) |
| Verify performance of new analytical test systems |
95% (225) |
| Participate in proficiency testing for PT testing |
91% (232) |
| Assure that clinician receives patient test results |
91% (229) |
| Periodically verify calibration of all instrumentation |
86% (212) |
| Compare instrument printout to reported patient value |
78% (183) |
| Compare patient value to previous values (delta check) |
73% (178) |
| Monitor rate of critical values reported |
45% (109) |
| Monitor rate of patient specimen redraws |
38% (93) |
| Monitor rate of patient test repeats |
32% (77) |
|
*Number refers to those responding affirmatively to each question
and proportions are the percent affirmative responses of all responding either
affirmatively or negatively to each question.
|
Given a list of 6 approaches to evaluate the competency of testing personnel,
participants were asked to indicate which they used. The following table
summarizes their responses.
|
|
Table 18 - Competency assessment
|
| Competency assessment activity |
Proportion (Number)* |
| Successful performance of QC |
97% (246) |
| Review of procedure manuals |
89% (226) |
| Direct observation of testing |
87% (219) |
| Participation in continuing education |
80% (201) |
| Analysis of unknown samples |
77% (193) |
| Periodic written examination |
26% (64) |
|
*Number refers to those responding affirmatively to each question
and proportions are the percent affirmative responses of all responding either
affirmatively or negatively to each question.
|
|
Onsite Visits
|
As part of this study, we also performed focused on-site reviews of PT testing
in 25 sites in the State of Washington. Any site that performed PT testing,
with a routine MTS survey due between November 2003 and June 2004, was included
in our sample. In addition, 1 review was performed during a validation survey
of a hospital accredited by the Joint Commission for Accreditation of
Healthcare Organizations and 1 as part of a complaint investigation. Fifteen
different instrument/reagent combinations (including traditional methods and
POC devices) were represented in this sample. During these onsite visits we
observed actual testing practices, reviewed written policies, worksheets,
patient test reports, manufacturer's product inserts and manuals, and
interviewed staff on problems and concerns related to their PT testing.
Thirteen of the 25 sites visited also completed the mailed questionnaire, and
we were able to validate their responses on the survey questions in that they
agreed using the 2 data collection approaches.
|
Discussion
|
One of the primary goals of this study was to determine if laboratory testing
personnel use voluntary practice standards to develop their policies and
practices. We focused on 4 areas important for PT testing:
-
anticoagulant concentration in the specimen collection tube,
-
specimen acceptance and rejection policy,
-
selection of reagent with low ISI, and
-
verification of the reference range and mean of normal of the reagents.
Of those responding, a minority (22-46%) stated using voluntary practice
standards. The most commonly mentioned standards were those developed by the
CLSI and CAP. Respondents relied on a variety of other resources for
establishing their policies and practices. Manufacturers recommendations,
journal articles, Government regulations, accreditation standards and corporate
policies were commonly noted. The most common reason given for not using
practice standards was lack of awareness (51-60%). Testing sites also said they
performed their own studies (24-31%) and searched the literature (19-32%).
Sites using POC devices commonly said that practice standards were not
applicable for their testing, because the tests were CLIA-waived, they used
finger stick specimens only, or that certain variables were pre-set by the
manufacturer. Very few respondents said they could not afford (8-10%) or did
not agree (0-1%) with practice standards.
Of the respondents performing venipuncture collections, 94% had a written
specimen acceptance/rejection policy. The vast majority of respondents (92%)
exclusively used the recommended sodium citrate concentration of 3.2%. For
sites using traditional testing methods, the majority (76%) used a reagent with
an ISI of <1.70, verified their reference range (92%), and established their
mean of normal (95%) for new lots of thromboplastin reagents.
For sites using POC devices, specimens are primarily obtained by finger stick
or capillary collection methods. The issues of collection tubes and transport,
processing, and storage of samples are not applicable in those cases.
Respondents using POC devices relied more on information provided by the
manufacturer for reference ranges and mean of normal values. The CLSI has a
proposed standard that addresses point-of-care monitoring of anticoagulation
therapy that can be a good resource for these testing sites (15).
By sharing this report with study participants, we hope to raise awareness of
practice guidelines and other references that may help to harmonize practices
among all sites performing PT testing. An awareness of laboratory practice
standards must also be raised by professional societies, including those
representing physicians, nurses, medical assistants, and others who commonly
perform laboratory testing as a component of their overall health care
activities. Sites using POC devices may benefit from the development of new
practice standards that are written with POC devices, settings and personnel in
mind. In addition, there needs to be an acknowledgement of a balance between
practice standards and other legitimate resources for the development of
harmonized practices between laboratories, such as manufacturer information,
Government regulations and accreditation organization standards.
Another primary goal of this study was to evaluate quality indicators in both
general laboratory practices and for PT testing specifically. By raising
awareness about common and best practices, it is hoped that testing personnel
may investigate and adopt new practices based on a comparison to their peers.
Throughout this report we acknowledge differences between POC and traditional
methods that have an effect on laboratory practice variables. When testing
occurs at point of care, the testing personnel have access to more patient
information than is typically available in a traditional hospital or an
independent laboratory setting. A review of the medical record and/or interview
with the patient may allow for the immediate assessment of test result
acceptability and timely resolution by specimen recollection, test repeat or
referral. The collection of capillary specimens alleviates several issues
related to transport, processing, storage and time delays that must be
addressed by the traditional laboratory setting. Manufacturers of POC devices
research practice guidelines as evidenced by their references to them in their
product inserts. For POC devices, the manufacturer addresses many QC and QA
activities: pre-set calibration and calculations, electronic controls,
instrument flagging, and established reference ranges. As a result, this allows
for less reliance on practice standards to develop policies and procedures,
fewer QC and QA activities by the user, and less rigorous programs for training
and competency assessment than for traditional testing methods.
Because clinicians compare patient INR values against standardized therapeutic
ranges and monitor trends in an individual patient's INR values over time,
consistency in test values from an individual laboratory and agreement in
values from different laboratories are issues of key importance. One very
vulnerable step in PT testing occurs when laboratories introduce new lots of
reagents. The laboratory may not recognize that the reagent sensitivity has
changed and may not perform studies to identify that the patient's INR values
may have shifted. Verification of the ISI value in the product insert with
every lot of reagents (whether a change is expected or not) is a simple, but
effective, solution to help alleviate serious calculation errors (16).
Laboratories should establish their own patient mean of normal when using new
reagents, and they should perform parallel testing between old and new lots.
Laboratories must assure that ISI and mean of normal values are correctly
entered into their instrument and laboratory information systems when
calculating INRs, and they must alert clinicians when there is a change in INR
values that may affect their ability to judge patients' coagulation status.
Consistency of test results between laboratories can be improved when sites use
reagents with low ISI values, when they use collection tubes with 3.2% sodium
citrate, and when they report PT results as INRs. Although not always feasible
and not required by CLIA, every site regardless of their setting or
methodology, should know how their INR values compare with those in another
site. It is common for near-patient settings to refer samples with questionable
critical values to another site for confirmation. Clinicians need to know where
test results are coming from and how results from different laboratories
compare.
In this study, we found that nearly a third (29%) of our respondents knew of PT
testing performed in another location in their facility. We also found that
only 42% of laboratories performing traditional methods and 40% of those using
POC devices performed a correlation with another method or site. By knowing the
bias between methods, testing personnel can judge the acceptability of their
own method and assist clinicians in judging the clinical significance of
differences in values obtained on an individual patient tested at the 2 sites.
In addition, both sites should communicate with each other and with clinicians,
whenever new methods or reagents are introduced that may change the established
bias. Another correlation study may be warranted in these instances. In one
published study, authors found that statistically INRs are clinically
equivalent if they are within 0.4 of a target value of 2.5 and within 0.7 of a
target value of 3.5 (17).
In a 2001 study commissioned by the Agency for Healthcare Research and Quality
to identify practices likely to improve patient safety, patient self-management
of warfarin therapy was identified as an intervention with strong evidence
supporting wide-spread implementation (18). In our study, we found this
practice to be uncommon (5% of respondents).
|
Authors' contributions: Both authors had access to all study data. Ms
LaBeau takes responsibility for the integrity of the data, and Dr Shahangian
accepts responsibility for the accuracy of data analyses.
Study concept and design: LaBeau, Shahangian
Acquisition of data: LaBeau
Analysis and interpretation of data: Shahangian, LaBeau
Drafting of the manuscript: LaBeau
Critical revision of the manuscript for important intellectual content: Shahangian,
LaBeau
Administrative, technical, or material support: LaBeau, Shahangian
Study supervision: LaBeau, Shahangian
|
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