The current status of urinary proteins as diagnostic and prognostic markers

Abstract

Numerous proteins appear in urine under different pathophysiological conditions. Individual proteins are measured by immunoassays, while mass spectrometry is being introduced to evaluate proteins and peptides. The protein in urine is more or less unstable and heterogeneous due to degradation or modification by urine proteases, resulting in altered immunochemical reactions. A quality assurance system for each analyte by each is a key, by setting proper pre-analytical conditions and establishing reference measurement systems, especially by qualified reference material. Indication for urine protein measurement is to seek pathogenesis, localisation of the affected organ or tissue, evaluation of prognosis or response to therapy in systemic, renal and genitourinary diseases. Albumin, a marker for glomerular dysfunction, is essential not only for diabetic nephropathy, but a reliable risk and prognostic marker for cardiovascular diseases. Measurement of very low levels is underway for early detection and prevention of related diseases. α1-microglobulin is a well-established reliable tubular marker. Among post-renal markers IL-8 is a good inflammatory marker especially for urinary tract infection (UTI). The pre-renal marker may specifically detect systemic diseases; a specific antibody against microorganisms is in use by point of care testing (POCT). Clinical usefulness is being expanded by discovery of new proteins and peptides that may be incorporated in the expert system.