Freezing method affects the concentration and variability of urine proteins and the interpretation of data on microalbuminuria. The Oxford Regional Prospective Study Group.

@article{citeulike:2873172, abstract = {AIMS: Microalbuminuria and, to a lesser extent, renal tubular proteins are widely used in the early detection of incipient nephropathy in diabetes mellitus. Recent reports have indicated detrimental effects of storage at -20 degrees C on urine proteins. This study investigated the effects of storage on the measurement of urine proteins and discusses implications for the interpretation of data. METHODS: Two-hundred and sixty-eight specimens, collected from children with Type 1 diabetes, split into duplicate aliquots and stored at -20 degrees C and -70 degrees C, respectively, for 6-8 months, were analysed for albumin, retinol binding protein, N-acetyl glucosaminidase and creatinine, in the same assays to eliminate inter-assay variability. Two independent non-diabetic cohorts of children provided urine specimens, which were stored at -20 degrees C for one cohort and -70 degrees C for the other, to determine normal ranges for urine proteins. RESULTS: Storage at -20 degrees C led to a variable underestimation of all three urine proteins in 20\% of specimens. Creatinine was unaffected. This underestimation was greater in more concentrated urine (r2 = 0.38, P < 0.001, n = 262). Consequently storage at -20 degrees C increased the variance of the albumin/ creatinine ratio more than the variance of albumin concentration. Temperature of storage affected the normal range, which was 0.1-2.1 mg/mmol at -20 degrees C compared to 0.3-3.1 mg/mmol at -70 degrees C. The prevalence of microalbuminuria (> 2SD above the geometric mean in non-diabetic specimens stored at -20 degrees C) was 27\% after storage at -70 degrees C vs. 24\% after -20 degrees C. The prevalence of microalbuminuria (>2SD above the geometric mean in nondiabetic specimens stored at -70 degrees C) was 21\% after storage at -70 degrees C vs. 17\% after -20 degrees C. CONCLUSIONS: Urine proteins are significantly but variably underestimated after storage at -20 degrees C. These effects account for increased variance and differences in the normal range, but have less effect on the detection of microalbuminuria than might be predicted.}, address = {Division of Public Health and Primary Health Care, Institute of Health Sciences, University of Oxford, UK.}, author = {Schultz, C. J. and Dalton, R. N. and Turner, C. and Neil, H. A. and Dunger, D. B. }, citeulike-article-id = {2873172}, issn = {0742-3071}, journal = {Diabetic medicine : a journal of the British Diabetic Association}, keywords = {proteinuria}, month = {January}, number = {1}, pages = {7--14}, posted-at = {2008-06-08 06:56:11}, priority = {2}, title = {Freezing method affects the concentration and variability of urine proteins and the interpretation of data on microalbuminuria. The Oxford Regional Prospective Study Group.}, url = {http://view.ncbi.nlm.nih.gov/pubmed/10691153}, volume = {17}, year = {2000} }

TY - JOUR ID - citeulike:2873172 L3 - citeulike-article-id:2873172 TI - Freezing method affects the concentration and variability of urine proteins and the interpretation of data on microalbuminuria. The Oxford Regional Prospective Study Group. JF - Diabetic medicine : a journal of the British Diabetic Association VL - 17 IS - 1 SP - 7 EP - 14 AD - Division of Public Health and Primary Health Care, Institute of Health Sciences, University of Oxford, UK. SN - 0742-3071 N2 - AIMS: Microalbuminuria and, to a lesser extent, renal tubular proteins are widely used in the early detection of incipient nephropathy in diabetes mellitus. Recent reports have indicated detrimental effects of storage at -20 degrees C on urine proteins. This study investigated the effects of storage on the measurement of urine proteins and discusses implications for the interpretation of data. METHODS: Two-hundred and sixty-eight specimens, collected from children with Type 1 diabetes, split into duplicate aliquots and stored at -20 degrees C and -70 degrees C, respectively, for 6-8 months, were analysed for albumin, retinol binding protein, N-acetyl glucosaminidase and creatinine, in the same assays to eliminate inter-assay variability. Two independent non-diabetic cohorts of children provided urine specimens, which were stored at -20 degrees C for one cohort and -70 degrees C for the other, to determine normal ranges for urine proteins. RESULTS: Storage at -20 degrees C led to a variable underestimation of all three urine proteins in 20% of specimens. Creatinine was unaffected. This underestimation was greater in more concentrated urine (r2 = 0.38, P < 0.001, n = 262). Consequently storage at -20 degrees C increased the variance of the albumin/ creatinine ratio more than the variance of albumin concentration. Temperature of storage affected the normal range, which was 0.1-2.1 mg/mmol at -20 degrees C compared to 0.3-3.1 mg/mmol at -70 degrees C. The prevalence of microalbuminuria (> 2SD above the geometric mean in non-diabetic specimens stored at -20 degrees C) was 27% after storage at -70 degrees C vs. 24% after -20 degrees C. The prevalence of microalbuminuria (>2SD above the geometric mean in nondiabetic specimens stored at -70 degrees C) was 21% after storage at -70 degrees C vs. 17% after -20 degrees C. CONCLUSIONS: Urine proteins are significantly but variably underestimated after storage at -20 degrees C. These effects account for increased variance and differences in the normal range, but have less effect on the detection of microalbuminuria than might be predicted. KW - proteinuria AU - Schultz, CJ AU - Dalton, RN AU - Turner, C AU - Neil, HA AU - Dunger, DB PY - 2000/01// UR - http://view.ncbi.nlm.nih.gov/pubmed/10691153 ER -