28 - Clinical Biochemistry of Renal Function

W. G. Guder Renal functions have been tested since ancient times. Recent advances in our knowledge and technical progress have challenged our strategy in analysing various renal functions. The example of proteinuria will be described in more detail. 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, a1-microglobulin, immunoglobulin G and a2-macroglobulin together with total protein, prerenal, glomerular, tubular and postrenal causes of proteinuria can be detected and differentiated by their specific urine protein patterns. Thus tubulo-interstitial diseases negative in the protein test strip procedure, are detected and clearly differentiated from other causes of proteinuria by their high a1-microglobulin/albumin ratios. Albumin in urine has been introduce as a marker of the quality of glomerular filtration, whereas the quantity can be calculated from a single measurement of Cystatin C in Plasma/Serum. In postrenal proteinuria, a2-macroglobulin proved to be a useful marker, when albumin excretion exceeds 100 mg/L urine. This protein exhibits plasma-like ratios to albumin in postrenal causes, whereas it is much lower in renal proteinurias. The high specificity of these new markers seems to reduce the importance of microscopic analysis of the urine sediment, challenged by the introduction of quantitative flow cytometry. The new strategy, which has been evaluated in more than 500 clinically and partly histologically proven cases of renal diseases allows to distinguish all clinically important causes of proteinuria and haematuria from analysis of a single morning spot urine sample.