Laboratory measurement of urine albumin and urine total protein in screening for proteinuria in chronic kidney disease.

Laboratory measurement of urine total protein has been important for the diagnosis and monitoring of renal disease for decades, and since the late 1990s, urine albumin has been measured to determine whether a diabetic patient has incipient nephropathy. Evolving understanding of chronic kidney disease (CKD) and, in particular, the cardiovascular risks that CKD confers, demands more sensitive detection of protein in urine. As well, evidence is now emerging that cardiovascular and all-cause mortality risks are increased at levels within the current 'normal' range for urine albumin. Standardisation is essential to permit valid application of universal decision points, and a National Kidney Disease Education Program/International Federation of Clinical Chemistry and Laboratory Medicine (NKDEP/IFCC) Working Party is making progress towards a reference system for urine albumin. In the meantime, available data suggest that Australasian laboratory performance is adequate in terms of precision and accuracy above current decision limits for urine albumin. In contrast, the complexity of proteins in urine makes standardisation of urine total protein measurement impossible. As well, urine total protein measurement is insufficiently sensitive to detect clinically important concentrations of urine albumin. An Australasian Expert Group, the Proteinuria Albuminuria Working Group (PAWG) has proposed that urine albumin/creatinine ratio is measured in a fresh, first morning, spot sample to screen for proteinuria in CKD. Both NKDEP/IFCC and PAWG emphasise the need for standardisation of sample collection and handling.