Schultz C J, Dalton R N, Turner C, Neil H A, Dunger D B
Division of Public Health and Primary Health Care, Institute of Health Sciences, University of Oxford, UK.
Diabet Med. 2000 Jan;17(1):7-14. doi: 10.1046/j.1464-5491.2000.00200.x.
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.
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.
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.
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.
微量白蛋白尿以及程度较轻的肾小管蛋白，被广泛用于糖尿病早期肾病的检测。最近的报告表明，在-20℃储存对尿蛋白有不利影响。本研究调查了储存对尿蛋白测量的影响，并讨论了对数据解读的意义。
从1型糖尿病儿童中收集268份标本，分成两份等分试样，分别在-20℃和-70℃储存6 - 8个月，对白蛋白、视黄醇结合蛋白、N - 乙酰氨基葡萄糖苷酶和肌酐进行分析，采用相同检测方法以消除检测间的变异性。两组独立的非糖尿病儿童队列提供尿标本，一组储存在-20℃，另一组储存在-70℃，以确定尿蛋白的正常范围。
在-20℃储存导致20%的标本中所有三种尿蛋白出现不同程度的低估。肌酐不受影响。在浓度较高的尿液中这种低估更明显（r2 = 0.38，P < 0.001，n = 262）。因此，在-20℃储存使白蛋白/肌酐比值的方差增加幅度大于白蛋白浓度的方差。储存温度影响正常范围，-20℃时为0.1 - 2.1mg/mmol，而-70℃时为0.3 - 3.1mg/mmol。在-70℃储存后微量白蛋白尿的患病率（高于储存在-20℃的非糖尿病标本几何平均数2个标准差以上）为27%，而在-20℃储存后为24%。在-70℃储存后微量白蛋白尿的患病率（高于储存在-70℃的非糖尿病标本几何平均数2个标准差以上）为21%，而在-20℃储存后为17%。
在-20℃储存后尿蛋白会被显著但不同程度地低估。这些影响导致方差增加和正常范围存在差异，但对微量白蛋白尿检测的影响小于预期。
