Background: Our objective was to quantify short-term total within-person variability in standard and nontraditional kidney measures using national data. Study Design: Repeated examination study of serum and urine kidney measures. Setting & Participants: Participants 18 years or older in the Third National Health and Nutrition Examination Survey (NHANES III) who had repeated blood and urine samples collected during visits occurring approximately 18 days apart. Measurements: Standardized serum creatinine, standardized cystatin C, β-trace protein (BTP), β2-microglobulin (B2M), and urine albumin and creatinine. We calculated the within-person coefficient of variation (CVw), which includes both biological and analytical variability. We also evaluated the impact of variability on estimates of the prevalence of reduced estimated glomerular filtration rate and albuminuria. Results: Serum cystatin C level demonstrated the lowest short-term within-person variability (CVw = 6.8%). Serum creatinine and B2M levels (CVw = 7.6% and 8.4%, respectively) also had low variability. BTP level had the most variability of the serum markers (CVw = 11.6%). As expected, urine albumin and urine creatinine measurements showed high variability (CV w >30% for both); however, albumin-creatinine ratio performed much better than either measure alone, with CVw of 11.3%. The effect of short-term variability on the prevalence of reduced estimated glomerular filtration rate was moderate, with an ∼20% lower prevalence when defined based on single measurements compared to repeated application of the same test approximately 18 days apart. Repeated testing for albuminuria had a larger effect, showing a 33% lower prevalence of albuminuria when repeated testing was applied. Limitations: Only 2 measurements available. General population with low prevalence of kidney disease. Conclusions: Our results suggest that creatinine, cystatin C, and B2M levels have similarly low short-term variability. BTP level was more variable compared with the other serum filtration markers. Urine albumin and creatinine levels were highly variable and may benefit from repeated assessments to reduce the misclassification of albuminuria.
Bibliographical noteFunding Information:
Support: Siemens Healthcare Diagnostics provided a grant to the University of Minnesota for labor and reagents to conduct the B2M and BTP and some cystatin C assays. This project was partially funded by National Institutes of Health (NIH)/National Institute of Diabetes and Digestive and Kidney Diseases grant U01 DK067651 . Mr Juraschek was supported by NIH/National Heart, Lung and Blood Institute grant T32 HL007024 .
- National Health and Nutrition Examination Survey (NHANES)
- beta 2 microglobulin
- beta trace protein
- cystatin C
- estimated glomerular filtration rate
- short-term variability