Liquid chromatography tandem mass spectrometry (LC-MS/MS) candidate reference measurement procedure for urine albumin

Urine albumin is a key biomarker utilized for diagnosis and monitoring progression of chronic kidney disease (CKD). These characteristics highlight the importance urine albumin serves in patient management. However, laboratory results are confounded by a lack of standardization where results may exceed 40 % difference between diagnostic platforms. This presents serious issues since current guideline clinical decision points are fixed values and misclassification may occur between laboratory methods. Therefore, standardization is needed for urine albumin measurements.

A liquid chromatography tandem mass spectrometry (LC-MS/MS) reference measurement procedure (RMP) was developed. This RMP employed proteolysis using trypsin and examined six peptides specific to human serum albumin. The National Institute of Standards and Technology 2925 reference material was used to value assign calibrators. To improve imprecision and accuracy, all samples were run in quadruplicate. Urine from 98 patient specimens was analyzed.

RMP final results consisted of averaging four peptide transitions, yielding a 20-day coefficient of variation (CV) of <3.0 %. Factors considered in assigning RMP overall uncertainty included specimen and internal standard pipetting, calibration material, and LC-MS/MS imprecision. This RMP was compared to the Roche Cobas and Siemens Dimension Vista urine albumin assays and was found to have a -9.9 and 20.1 % bias, respectively. This RMP was found to have equivalent results to two other RMPs in a previous study.

This RMP demonstrated excellent imprecision, achieving an overall CV of 2.8 % and meeting the CV ≤6.2 % performance specification required for standardizing urine albumin measurements in clinical laboratories.