Urinary protein/creatinine ratio before and during pregnancy in women with diabetes mellitus

Quantitation of urinary protein excretion has traditionally involved collection of a 24-hour urine specimen. Recent reports have suggested that the ratio of protein to creatinine in a single-voided urine specimen may be used as a screening test of proteinuria, obviating the need for a 24-hour urine collection. This study was undertaken to determine whether the urinary protein/creatinine ratio was correlated with 24-hour protein excretion in women with diabetes, to determine whether pregnancy had any effect on the correlation, and to test the accuracy of estimates of 24-hour protein excretion on the basis of the protein/creatinine ratio. We studied 329 24-hour urine specimens from 133 women with classes B through RF diabetes. The protein/creatinine ratio was highly correlated with total protein excretion (r = 0.977, p \lt 0.0001). The correlation was not affected by pregnancy, trimester, or preeclampsia. Three methods were used to predict protein excretion on the basis of the ratio. Compared with actual protein excretion, predicted values had mean errors of 19% to 27%; 6% to 13% of predictions were in error by ≥50%. Because of these large errors, we conclude that this method of estimating protein excretion has limited value in pregnant women with diabetes.