Comparative analysis of commercially available methods for proteinuria assessment from the medical decision point of view – what do we keep forgetting about

Abstract

Introduction: In assessing the kidney function Proteinuria still appears to be the most common screening test. Although recommendations focus on albuminuria, also in association with urine creatinine level, tradition, habits and economical reasons determine wide use of dipstick tests the tool for determining urine protein during routine urinalysis. Aim: The aim of this study was to compare 3 methodologically different tests used for assessing proteinuria, from medical point of view: the qualitative Sorenson method and 2 quantitative methods: the traditional Exton method and the method with pyrogallol red. Material and Methods: In this study we analyzed 395 urine samples from patients aged 3-101 years old, 45% (n=182) men, ordered from 18 entities. In all the samples we determined protein concentration with use of: Combur Test M dipstic tests, cobas u411, Roche; The Exton Reagent, Specol 11, Aqua-Med; Urinary/CSF protein, AU640, Beckman Coulter. Additionally we performed microscopic examination of urinary sediment and assessed if any physical or morphological parameters or the patients’ condition influence differences in obtained protein levels. Results: Analyzing the results we noticed the Sorenson method had tendency to generate ambiguous and inflated results in comparison to quantitative methods. The automatic method with pyrogallol red was characterized with the smallest imprecision across all its analytical linearity. Both quantitative methods was characterized with very good correlation coefficient (R=0.97) of results. The color of the urine, presence of bacteria and casts as well as serum C-reactive protein and creatinine level, and GFR were associated with statistically relevant differences in protein levels obtained with use of analytical methods in question. Conclusions: Only quantitative methods appear to ensure obtaining reliable proteinuria assessment. Laboratories should consider providing automatic quantitative methods for determining the concentration of the urine protein in routine urinalysis.