Clinical relevance of different electrophoretic methods for the analysis of urinary proteins.

Three electrophoretic techniques are usually available in the clinical laboratories for the qualitative investigation of urinary protein patterns: 1) acetate cellulose, 2) immuno-electrophoresis; and 3) SDS-polyacrylamide gel electrophoresis. Proteinuria (the excretion of proteins in excess of 150 mg/day or 100 microgram/min) usually signifies either increased permeability of the glomerular-capillary membrane of diminished tubular reabsorption. Since glomerular disease is associated with an increased clearance of albumin and higher molecular weight proteins, whereas tubular damage is associated with the predominant excretion of proteins of lower molecular weight than albumin, it seems logical to establish a classification of proteinuria according to the molecular weight of its constituents. One can thus basically distinguish 5 types of proteinurias: 1) physiological; 2) tubular; 3) selective glomerular; 4) non selective glomerular; and 5) mixed proteinurias. Additionally one must distinguish "myeloma proteinurias" where monoclonal complete or incomplete gamma-globulins are found in the urine. Clinically it may be useful to determine the qualitatively normal or pathologic character of a quantitatively normal proteinuria, especially in the following conditions: 1) for early diagnosis of nephropathy in patients, such as diabetics, which are particularly prone to suffer from renal complications; 2) to confirm the clinical cure or to predict the recurrence of renal diseases; and 3) in such situations as orthostatic, or myeloma proteinuria, or any elevation of the urinary protein output of unknown etiology.