Prolonged Frozen Storage of Urine Reduces the Value of Albuminuria for Mortality Prediction

Albuminuria is increasingly recognized as a cardiovascular risk factor in patients with diabetes and in the general population. Cardiovascular disease risk increases continuously with increasing urinary albumin excretion, starting at concentrations that once were considered healthy (1). We recently reported that, after prolonged frozen storage of urine samples, albumin concentrations may decrease, particularly those within the reference and microalbuminuric intervals(2). We also observed sample variation in the extent to which urinary albumin concentrations (UAC) decreased. In 2005, to investigate whether outcome predictions based on albuminuria were affected by assessment of UAC from frozen samples, we reassessed UAC in Prevention of Renal and Vascular ENdstage Disease (PREVEND) study baseline urine samples, collected and stored frozen at −20 °C from 1997 to 1998. The PREVEND study was approved by the local medical ethics committee and conducted in accordance with the guidelines of the Declaration of Helsinki(3).The PREVEND dataset was enriched for albuminuria. To create a representative sample of the general population, the enriched subset (UAC >10 mg/L) was …