Comparative Analysis of Urinary Total Proteins by Bicinchoninic Acid and Pyrogallol Red Molybdate Methods

Abstract

Background: The concentration of total proteins in urine is a good index of renal function, but its determination is found to be unreliable. The pyrogallol red molybdate (PRM) method for urine total proteins is being widely used in most of the hospitals because of its high sensitivity, better precision and its practicability. Bicinchoninic acid method (BCA) is also used for protein estimation and there have been no studies comparing this method with the PRM method in human urine samples. BCA method overestimates the urinary protein concentration in the presence of interfering substances. After removing the interfering substances present in the human urine samples the results of BCA method were compared with the PRM method. Aim: The purpose of the study is to identify whether the results of urine total proteins by BCA method are comparable to PRM method and can be used as an alternative to the PRM method. Setting and Design: This is a cross-sectional study done on fresh urine specimens from the hospital laboratory, covering a wide range of protein concentrations. Material and Methods: Fresh urine specimens covering a wide range of protein concentrations (urine dipstick: nil, trace, 1+, 2+ and ≥ 3+) of 36 patients were analysed by both the methods. Statistical Analysis: Imprecision was determined by repeated analysis study and Inaccuracy was assessed by comparing the results of the patient’s urine samples by both the methods using correlation plots, Bland and Altman, and Passing and Bablok regression analyses. Results: The coefficient of variation and mean (SD) for the BCA method were 4.6% and 799.1 (882.5) mg/L and for the PRM method were 5.1% and 802.1 (911.9) mg/L. The Pearson correlation coefficient, r was 0.93 (p < 0.0001). Method agreement studies showed no significant constant and proportional bias between both the methods. Conclusion: In urine which is subjected to removal of interfering substances, the BCA results are comparable to PRM method.

Keywords

• bland and altman analysis
• correlation
• passing and bablok regression analysis
• urinary protein assays