STORAGE-TEMPERATURE AND DIFFERING METHODS OF SAMPLE PREPARATION IN THE MEASUREMENT OF URINARY ALBUMIN

Microalbuminuria is a predictor of persistent proteinuria, renal failu re and cardiovascular disease and therefore accurate determination of urinary albumin concentration is important. We examined the stability of albumin in urine under different conditions of storage, temperature and sample preparation. There was no significant difference in urinar y albumin concentration between fresh urine and urine stored at either 4-degrees-C or 20-degrees-C for up to 7 days. Similarly in urine samp les from diabetic patients there was no significant difference in albu min concentration at levels ranging from 1.3 to 1999.3 mg/l between fr esh urine at 4-degrees-C and urine stored frozen for 1 week, 1 month o r 6 months. Neither storage temperature (-20-degrees-C or -40-degrees- C) nor centrifugation of sample prior to assay made a significant diff erence to the albumin concentration. Multiple freezing and thawing of urine samples during 6 weeks of storage at -20-degrees-C made no diffe rence to albumin concentrations. Storage of urine samples in either po lypropylene, polystyrene or borosilicate glass tubes did not result in a significant change in urinary albumin concentration after either 1 week or 1 month at -20-degrees-C although, after 1 month of storage, u rinary albumin concentrations tended to be lower by an average of appr oximately 7 %. In tubes to which gelatine had been added this was redu ced to 4 %. We conclude that fresh urine can be kept at 4-degrees-C or 20-degrees-C for up to 7 days. Frozen urine samples can be stored for up to 6 months before assay without any loss of albumin concentration . Polypropylene, polystyrene or borosilicate glass tubes are acceptabl e containers for short-term storage and samples can simply be thorough ly thawed and vortex mixed immediately prior to assay.