Validation of a method for analyzing urinary Cystatin C and analysis of ULSAM-77 urine samples

Abstract: Objective New biomarkers for acute kidney injury are needed and urinary Cystatin C is one alternative. The objective was to validate a urinary Cystatin C method on Mindray BS-380 comparing urine samples from the Uppsala Longitudinal Study of Adult Men (ULSAM-77) and urine samples from a reference group for Cystatin C. A visual control for a relationship between Cystatin C and C-reactive protein (CRP) and interleukin 6 (IL-6) respectively was made. Methods Precision, linearity, recovery, interference, and stability of the urine cystatin C method were investigated. Comparisons were made between ULSAM-77 samples and a reference group samples consisting of ordinary people. Results The highest total imprecision was 10.24 % for the sample with the lowest concentration. The second lowest concentration had 4.21 % total variation coefficient. The linearity equation was y = 0.99x – 0.01 with an R2-value of 0.99. The recovery for all concentrations was always 91 % or more. No interference from hemoglobin at a concentration of 10 g/L was found. The samples were stable at +5°C for seven days. The median for the samples from ULSAM-77 was 0.09 mg/L and the median for the reference samples was 0.06 mg/L. There was no obvious relationship between Cystatin C and CRP/IL-6 from ULSAM-77. Conclusion   Reliable data of urinary Cystatin C can be analyzed on a Mindray BS-380. The level of urinary Cystatin C was higher for people age 77 than for those with a median age of 49. There was no correlation between the concentration of Cystatin C in urine and the levels of CRP and IL-6.