Screening for microalbuminuria in patients with diabetes mellitus: frozen storage of urine samples decreases their albumin content
Elving, L.D.; Bakkeren, J.A.; Jansen, M.J.; de Kat Angelino, C.M.; de Nobel, E.; van Munster, P.J.
Clinical Chemistry 35(2): 308-310
1989
ISSN/ISBN: 0009-9147 PMID: 2914381 Document Number: 344247
The influence of storage on urinary albumin concentration was prospectively studied with use of overnight urine specimens (Albustix negative) from 73 diabetic patients. From each urine sample four aliquots were taken. One was stored at 4.degree. C and assayed within two weeks, the other three were stored at -20.degree. C and assayed within two weeks and after two and six months. Albumin concentration was measured with laser immunonephelometry. The detection limit, 1 mg/L, suffices for the screening of diabetic patients for microalbuminuria. After storage for two and six months at -20.degree. C, significantly lower albumin concentrations were found. The difference was mainly caused by lower concentrations found in urine samples in which a precipitate had formed, which was the case in 22 and 25 samples, respectively. Thus, freezing of urine samples for determination of low concentrations of albumin may yield falsely low results. Urine samples are best stored at 4.degree. C and assayed within two weeks.