National Health and Nutrition Examination Survey

1999-2004 Data Documentation, Codebook, and Frequencies

Glycated albumin, Beta-2 Microglobulin, Cystatin C (Surplus) (SSCARD_A)

Data File: SSCARD_A.xpt

First Published: June 2021

Last Revised: July 2022

Note: The NHANES Biospecimen Program processes were reevaluated in 2021 and 2022 to monitor quality control after a procedural error was identified. This error did not pose any risk of participant disclosure. Addressing this error resulted in the removal of some records from various stored biospecimen data files between 1999 and 2018 that did not meet program standards. After a comprehensive review of all stored specimen datasets, this data file was modified to remove records {5-<10% of records} that were initially included in error. No data values were altered. However, survey weights were newly created. For each analyte included in this data file, it was determined that overall and for stratified sex, age, and race/Hispanic origin groups, the updated file using the new sample weights resulted in an estimate within the 95% confidence limit calculated using the original file and sample weights. However, not all possible analyses were performed.

Component Description

Sera from stored surplus specimens in the NHANES 1999-2004 cycles were tested for glycated albumin, beta-2 microglobulin, and cystatin C.

Eligible Sample

NHANES participants aged 1 year or older who consented to storing their samples for future research and had stored samples from 1999-2004.

Description of Laboratory Methodology

This stored specimen study was conducted by the Principal Investigator (PI) Dr. Elizabeth Selvin at the Johns Hopkins Bloomberg School of Public Health. All measurements were performed during 2018-2020 at the University of Maryland School of Medicine, Baltimore, Maryland (Lab Director: Dr. Robert Christenson).

Glycated Albumin

Glycated albumin (and albumin) were measured in serum. Glycated albumin was measured using a complex method by Asahi Kasei Pharma (Lucica-GA-L) adapted to the Siemens Dimension Vista 1500 (Siemens Healthcare Diagnostics). The assay requires separate measurements of total albumin (bromcresol purple) and glycated albumin (enzymatic method utilizing ketoamine oxidase and an albumin-specific protease). The glycated albumin result is expressed as a percentage of total albumin (Formula: [((glycated albumin concentration in g/dL / serum albumin concentration in g/dL)/1.14)*100] + 2.9).

Most measurements were conducted in surplus sera samples that had not previously undergone freeze-thaw (i.e., pristine samples). However, pristine samples were not available in some participants and thus non-pristine samples were used for the remaining measurements.

CVs: albumin 2.92% (low, 4.27-5.21 g/dL) and 5.12% (high, 4.25-5.19 g/dL); glycated albumin, 4.93% (low, 0.56-0.758 g/dL) and 8.48% (high, 1.59-1.944 g/dL).

The glycated albumin and serum albumin test results are expressed in g/dL. The final glycated albumin result is expressed as a percentage per the formula above.

Beta-2 microglobulin

β–2 Microglobulin (β2M) was measured in serum using a B2M immunoassay (Siemens Healthcare Diagnostics) on an automated multi-channel analyzer, Siemens Dimension Vista 1500 (Siemens Healthcare Diagnostics). The lower and upper limits of detection are (0.72 mg/L, 23.0 mg/L).

CVs: 3.88% (med, 1.78-2.4 mg/L) and 3.42% (high, 4.49-6.07 mg/L).

The β2M result is expressed as mg/L.

Cystatin C

Cystatin C was measured in serum using a Cystatin C immunoassay (Siemens Healthcare Diagnostics) on an automated multi-channel analyzer, Siemens Dimension Vista 1500 (Siemens Healthcare Diagnostics). The lower and upper limits of detection are (0.23 mg/L, 8.00 mg/L).

CVs: 3.54% (low, 0.77-1.15 mg/L) and 4.36% (high, 1.61-2.41 mg/L)

The cystatin C result is expressed as mg/L.

Data Processing and Editing

Data were received after all analyses were complete. The data were not edited.
Data Access: All data are publicly available.

Analytic Notes

Detection Limits
Two variables are provided for each analyte. The variable name ending in “L” (ex., SSB2ML) indicates whether the result was either measurable, below the lower limit of detection (LLOD) or above the upper limit of detection (ULOD): A “0” value means that the result was measurable. A “1” indicates that the result was below the LLOD. A “2” indicates that the result was above the ULOD. For analytes with analytic results below the limit of detection (ex., SSB2ML=1), an imputed fill value was placed in the analyte results field. This value is the limit of detection divided by square root of 2 (LOD/√2). The other variable prefixed SS (ex., SSB2M), provides the analytic result for that analyte.

An indicator variable is included for whether the analyte was measured in a pristine sample (never thawed): 0=non-pristine;1=pristine. Analysts should consider limiting analyses of glycated albumin in NHANES 1999-2004 to pristine samples only. While the performance of the glycated albumin assay in the pristine samples (never thawed) was excellent, performance in non-pristine samples (at least 2 freeze-thaw cycles) was problematic (Daya, 2022).

The limits of detection (LODs) for B2M, CYST and ALB are:

Variable Name	Analyte name	LOD
SSB2M	Beta 2 Microglobulin, mg/L	0.72 mg/L, 23.0 mg/L
SSCYST	Cystatin C, mg/L	0.23 mg/L, 8.00 mg/L
SSGALB	Glycated Albumin, g/dL	-
SSALB	Albumin, g/dL	-
SSGALBP	Percent glycated albumin, %	-

Subsample Weights

Sample weights are required to analyze these data properly. Specific sample weights for this subsample are included in this data file and should be used when analyzing these data. When observations were removed from this data file, new sample weight were created and added to this data file (WTSSCB2Y, WTSSCB4Y). Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial for further details on the use of sample weights and other analytic issues.

The work was funded by a grant (PI: Elizabeth Selvin) received by the Johns Hopkins Bloomberg School of Public Health from the Biomarkers Consortium of the Foundation for the National Institutes of Health (FNIH).

References

Daya NR, Rooney MR, Tang O, Coresh J, Christenson RH, Selvin E. Glycated Albumin in Pristine and Non-Pristine Stored Samples in the National Health and Nutrition Examination Survey (NHANES) 1999–2004. The Journal of Applied Laboratory Medicine. 2022;7(4):916-922.
Kohzuma T, Yamamoto T, Uematsu Y, Shihabi ZK, Freedman BI. Basic performance of an enzymatic method for glycated albumin and reference range determination. Journal of diabetes science and technology. 2011;5(6):1455-1462.

Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:: SEQN
SAS Label:: Respondent sequence number
English Text:: Respondent sequence number.
Target:: Both males and females 1 YEARS - 150 YEARS

WTSSCB2Y - Cardiac biomarkers 2 year weights

Variable Name:: WTSSCB2Y
SAS Label:: Cardiac biomarkers 2 year weights
English Text:: Surplus specimen cardiac biomarkers 2 year weights
Target:: Both males and females 1 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
1250.055251 to 297328.56282	Range of Values	21890	21890
0	No lab specimen	0	21890
.	Missing	0	21890

WTSSCB4Y - Cardiac biomarker 4 yr weights 1999-2002

Variable Name:: WTSSCB4Y
SAS Label:: Cardiac biomarker 4 yr weights 1999-2002
English Text:: Surplus specimen cardiac biomarker 4 yr weights 1999-2002
Target:: Both males and females 1 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
773.99041 to 120568.91688	Range of Values	14656	14656
0	No lab specimen	0	14656
.	Missing	7234	21890

SSB2M - Beta 2 Microglobulin, mg/L

Variable Name:: SSB2M
SAS Label:: Beta 2 Microglobulin, mg/L
English Text:: Beta 2 Microglobulin, mg/L
Target:: Both males and females 1 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
0.509 to 23	Range of Values	21863	21863
.	Missing	27	21890

SSB2ML - Beta 2 Microglobulin comment code

Variable Name:: SSB2ML
SAS Label:: Beta 2 Microglobulin comment code
English Text:: Beta 2 Microglobulin comment code
Target:: Both males and females 1 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0	Within the detection limits	21824	21824
1	Below lower detection limit	15	21839
2	Above upper detection limit	24	21863
.	Missing	27	21890

SSCYST - Cystatin C mg/L

Variable Name:: SSCYST
SAS Label:: Cystatin C mg/L
English Text:: Cystatin C mg/L
Target:: Both males and females 1 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
0.163 to 8	Range of Values	21848	21848
.	Missing	42	21890

SSCYSTL - Cystatin C comment code

Variable Name:: SSCYSTL
SAS Label:: Cystatin C comment code
English Text:: Cystatin C comment code
Target:: Both males and females 1 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0	Within the detection limits	21824	21824
1	Below lower detection limit	22	21846
2	Above upper detection limit	2	21848
.	Missing	42	21890

SSGALB - Glycated Albumin g/dL

Variable Name:: SSGALB
SAS Label:: Glycated Albumin g/dL
English Text:: Glycated Albumin g/dL
Target:: Both males and females 1 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
0.039 to 6.452	Range of Values	21842	21842
.	Missing	48	21890

SSGALBL - Glycated Albumin comment code

Variable Name:: SSGALBL
SAS Label:: Glycated Albumin comment code
English Text:: Glycated Albumin comment code
Target:: Both males and females 1 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0	Within the detection limits	21842	21842
1	Below lower detection limit	0	21842
2	Above upper detection limit	0	21842
.	Missing	48	21890

SSALB - Albumin g/dL

Variable Name:: SSALB
SAS Label:: Albumin g/dL
English Text:: Albumin g/dL
Target:: Both males and females 1 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
0.059 to 7.583	Range of Values	21837	21837
.	Missing	53	21890

SSALBL - Albumin comment code

Variable Name:: SSALBL
SAS Label:: Albumin comment code
English Text:: Albumin comment code
Target:: Both males and females 1 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0	Within the detection limits	21837	21837
1	Below lower detection limit	0	21837
2	Above upper detection limit	0	21837
.	Missing	53	21890

SSGALBP - Percent glycated albumin%

Variable Name:: SSGALBP
SAS Label:: Percent glycated albumin%
English Text:: Percent glycated albumin%
Target:: Both males and females 1 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
3.537 to 1068.912	Range of Values	21815	21815
.	Missing	75	21890

SSPRIS - Pristine sample

Variable Name:: SSPRIS
SAS Label:: Pristine sample
English Text:: Pristine sample
Target:: Both males and females 1 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative
0	Non-Pristine	1674	1674
1	Pristine	20216	21890
.	Missing	0	21890

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