Detection and measurement of urinary protein

Abstract

The measurement of urine total protein and albumin is central to the diagnosis and management of subjects with kidney disease and in assessing cardiovascular risk. Accurate assessment is vital to enable detection and management of the patient with proteinuria. The spot urine protein has been suggested as an acceptable alternative to 24-h urine collections. Recent studies suggest that this holds true for screening to exclude significant proteinuria (>1 g/day) but data are lacking for the quantification of proteinuria and in assessing response to therapy. For albuminuria, while 24-h urinary albumin excretion remains the gold standard, spot urine samples are appropriate for screening. The optimal technique for the laboratory determination of urinary albumin has been questioned with the high-performance liquid chromatography-based method demonstrating significantly more albumin in the urine. Population-based studies have found dramatic increases in the prevalence of microalbuminuria with the new high-performance liquid chromatography assay. Whether this extra immunounreactive albumin detected by high-performance liquid chromatography is clinically important remains to be established. Twenty-four-hour urine collection remains the gold standard for the accurate determination of both total urinary protein and albumin. Spot urine samples can be used for screening patients for albuminuria and proteinuria. The optimal method for measuring urinary albumin concentration remains to be established.