Evaluation of five immunoturbidimetric assays for urinary albumin quantification and their impact on albuminuria categorization

Objectives: The study was designed to evaluate the performance of five automated immunoturbidimetric assays to quantify urinary albumin, each corresponding to a combination of a reagent and an analyzer (Olympus on AU640, Roche on Cobas Integra, Abbott on Architect, Ortho-Clinical Diagnostics Vitros on Fusion and Siemens on Dimension).

Design and methods: To assess imprecision, albumin was measured in three urinary pools with a mean value of 25, 66 and 131 mg/L. One hundred and eight patient urine samples were then used to compare each turbidimetric method using the Passing-Bablok regression and Bland-Altman analyses. Concordance of the albumin/creatinine ratio (ACR), according to the albuminuria classifications proposed by the KDIGO, was calculated to test the agreement between the different assays.

Results: All immunoturbidimetric methods evaluated in this study exhibited acceptable imprecision (CV<6%). Mean values for 108 urine samples varied from 0.5 to 762.2 mg/L. Significant differences were found (p<0.05) between all methods except between Olympus and Ortho (p=1.0) and between Abbott and Roche (p=0.12). Regarding the albuminuria categories based on the ACR proposed by the KDIGO, only the classification obtained with the Roche method was significantly different from the four other methods (p<0.001).

Conclusions: We demonstrated that all assays were not strictly equivalent which could affect ACR categories in clinical practice, suggesting the need for harmonization of commercial methods.