National Health and Nutrition Examination Survey

1999-2000 Data Documentation, Codebook, and Frequencies

Cystatin C - Serum (Surplus) (SSCYST_A)

Data File: SSCYST_A.xpt

First Published: June 2008

Last Revised: April 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. The sample weights and overall estimates were compared between the original and revised files. The sample weights provided with the original data release are appropriate to use with this updated data file; therefore, no new survey weights were created. The overall estimates from these files were examined and are consistent with the previous file. However, not all possible analyses were performed. For any queries related to this dataset please email the Biospecimen Program at serumplasmaurine@cdc.gov.

Component Description

Cystatin C assayed from stored serum samples from NHANES 1999-2000.

Eligible Sample

All participants aged 60+ with available specimen and a 25% random sample of participants aged 12-59 years. This younger group is supplemented with all individuals with high serum creatinine 1.2 mg/dl in men and >1.0 mg/dl in women) after calibration.

Description of Laboratory Methodology

All assays were conducted using the Dade Behring N Latex Cystatin C assay which is an automated particle-enhanced nephelometric assay (PENIA) run on the Dade Behring Nephelometer II (BNII) (1).

Data Processing and Editing

All data will be made publicly available.

Laboratory Quality Assurance and Monitoring

This assay has an intra-assay imprecision of 2.0 - 3.0% coefficient of variation and an inter-assay imprecision of 3.2 - 4.4% coefficient of variation. The assay range is 0.23 - 7.25 mg/dL. A thorough review of different assay methodologies by Newman (2) concluded that it is the most precise automated assay across the clinical concentration range and performed slightly better than the other automated assays in terms of sensitivity and lack of analytical interference.

Analytic Notes

The sub-sample of participants aged 12-59 requires modification of original sampling weights. Weights will be provided by investigators to NCHS and will be adjusted by age, sex, race, and serum creatinine strata to match the original NHANES 1999-2000 design.

Acknowledgement

This research was supported by NIH grants UO1 DK 053869, UO1 DK 067651, and UO1 DK 35073.

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 12 YEARS - 150 YEARS

SSCYPC - Cystatin C (mg/L)

Variable Name:: SSCYPC
SAS Label:: Cystatin C (mg/L)
English Text:: Cystatin C (mg/L)
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
0.47 to 7.15	Range of Values	2471	2471
.	Missing	37	2508

WTSCY4YR - Surplus sera cystatin 99-02 weights

Variable Name:: WTSCY4YR
SAS Label:: Surplus sera cystatin 99-02 weights
English Text:: Surplus sera cystatin 99-02 weights
Target:: Both males and females 12 YEARS - 150 YEARS

Code or Value	Value Description	Count	Cumulative	Skip to Item
0 to 418199.9809	Range of Values	2508	2508
.	Missing	0	2508

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