BACKGROUND: Microalbumin has assumed an increased role in the early diagnosis, assessment, and treatment of diabetic kidney disease. The microalbumin stability during urine storage for extended periods remains controversial. The purpose of the present investigation was to study the effects of storage at various conditions and for various periods on measurements of albumin in urine. METHODS: We measured microalbumin by immunonephelometry of Behring 100 system. We divided each of 99 urine samples into three aliquots: The first aliquot from each sample was used to measure micoralbumin in fresh urines (group 1), refrigerated at 4degrees C for one week (group 2) and three weeks (group 5), and analyzed for microalbumin; the second aliquot from each sample was frozen at -20degrees C for one week (group 3) and three weeks (group 6), thawed, not mixed, and analyzed for microalbumin; the third (group 7), aliquot from each sample was frozen at -20degrees C for one week (group 4) and three weeks (group 7), but mixed before measuring microalbumin. RESULTS: Samples from groups 2, 4, 5, and 7 showed no significant change in microalbumin concentration compared with the original value in group 1. In contrast, the values for groups 3 and 6 were significantly lower compared with those for group 1 (P<0.05). CONCLUSIONS: Microalbumin in urine is stable at 4degrees C for at least 3 weeks. And urine samples can be safely frozen at -20degrees C if they are mixed after thawing immediately before assay.