Long-Term Longitudinal Stability of Kidney Filtration Marker Measurements: Implications for Epidemiological Studies and Clinical Care.

Background: Establishment and improvement of glomerular filtration rate estimating equations requires accurate and precise laboratory measurement procedures (MPs) for filtration markers. The Advanced Research and Diagnostic Laboratory (ARDL) at the University of Minnesota, which has served as the central laboratory for the Chronic Kidney Disease Epidemiology Collaboration since 2009, has implemented several quality assurance measures to monitor the accuracy and stability of filtration marker assays over time.

Methods: To assess longitudinal stability for filtration marker assays, a 40-sample calibration panel was created using pooled serum, divided into multiple frozen aliquots stored at -80 °C.

Performance in Measurement of Serum Cystatin C by Laboratories Participating in the College of American Pathologists 2014 CYS Survey.

Context: Cystatin C is becoming an increasingly popular biomarker for estimating glomerular filtration rate, and accurate measurements of cystatin C concentrations are necessary for accurate estimates of glomerular filtration rate.

Objective: To assess the accuracy of cystatin C concentration measurements in laboratories participating in the College of American Pathologists CYS Survey.

Design: Two fresh frozen serum pools, the first from apparently healthy donors and the second from patients with chronic kidney disease, were prepared and distributed to laboratories participating in the CYS Survey along with the 2 usual processed human plasma samples.

The effects of freeze-thaw on β-trace protein and β2-microglobulin assays after long-term sample storage.

Objectives: To evaluate the effect of a freeze-thaw cycle on β-trace protein (βTP) and β2-microglobulin (β2M).

Design And Methods: We compared βTP and β2M concentrations before and after a single freeze-thaw cycle in long-term stored samples from 172 participants of the Third National Health and Nutrition Examination Survey (NHANES III).

Results: Measurements of βTP and β2M before and after freeze-thaw were highly correlated with Spearman's coefficients of 0.

Determining stability of stored samples retrospectively: the validation of glycated albumin.

Background: Determining the stability of stored samples for assays that were not available at the time of original collection is problematic. To assess sample stability for a relatively new assay of glycated albumin (GA), we first measured GA in fresh samples and in samples stored for 19-23 years. We then compared the regression of the contemporaneous glycohemoglobin (Hb A(1c)) values against the GA results from fresh vs stored samples, reasoning that similar slopes and intercepts would provide strong, albeit indirect, support for the stability of the stored samples for GA measurements.