Electrophoretic pattern of concentrated urine: comparison between 24-hour collection and random samples

The electrophoretic pattern of concentrated urine samples can be used to identify the type of proteins leaking into the urine and has diagnostic and prognostic value, providing information about the location (glomerular or tubular) and degree of renal injury. This test usually requires a 24-hour urine collection, which can be inconvenient because of its heavy dependence on patient compliance and frequently is unreliable because of errors in collecting a complete 24-hour urine sample. In this study, we compared the electrophoretic pattern in 24-hour urine collections and random samples among patients with glomerular diseases and a wide range of proteinuria. Forty adult patients were evaluated; 24-hour urine collections and random urine samples were analyzed. Protein concentrations were determined using the sulfosalicylic acid method standardized with human serum. Electrophoresis was performed with concentrated urine samples (Ultrafree, PF/Millipore Corporation, Bedford, MA) using Beckman Paragon Electrophoresis System (agarose gels and blue staining; Beckman Instruments, Inc, Brea, CA). Densitometric scanning of electrophoretic pattern (Appraise Clinical Densitometer; Beckman Instruments, Inc) was performed, and the results were reported in percentages of each observed fraction. Our results revealed that despite the significant difference between protein concentration in 24-hour collections and in random samples, the pattern of protein excretion, in percentage basis, remains the same. There were no differences between the albumin, alpha(1)-globulin, alpha(2)-globulin, beta-globulin, and gamma-globulin fractions in both types of specimens. This study shows that, at least in glomerular proteinuria, the electrophoretic analysis of the urine can be performed accurately in random samples, avoiding the inconveniences and errors of a 24-hour urine collection.