Physiopathology of proteinuria and laboratory diagnostic strategy based onsingle protein analysis

A quantification of proteins of different molecular size has been shown to be useful in characterizing the mechanism and medical causes of proteinuria . By analyzing urine albumin, alpha(1)-microglobulin, immunoglobulin G and alpha(2)-macroglobulin together with total protein, prerenal, glomerular, t ubular and postrenal causes of proteinuria can be detected and differentiat ed by their specific urine protein patterns. Using automated turbidimetric procedures, prerenal proteinurias are characterized by an albumin/total pro tein ratio below 0.4. Tubulo-interstitial diseases which are negative in th e protein test strip procedure are detected and clearly differentiated from other causes of proteinuria by their high alpha(1)-microglobulin/albumin r atios. In postrenal proteinuria, alpha(2)-macroglobulin proved to be a usef ul marker, when albumin excretion exceeds 100 mg/l urine. This protein exhi bits plasma-like ratios to albumin in postrenal causes, whereas it is much lower in renal proteinurias. The new strategy, which has been evaluated in more than 500 clinically and partly histologically proven cases of renal diseases, more sensitively dete cts glomerular and tubulo-interstitial diseases when applied in urine scree ning and allows us to distinguish all clinically important causes from anal ysis of a morning spot urine sample.