Aim: Dipstick results for proteinuria are affected by urine concentration, and thus urine creatinine concentration ([Cr]). This study was performed to determine whether spot urine [Cr] changes significantly during pregnancy, leading to a significantly different false-negative rate (FNR) on dipstick test between trimester.
Methods: The [Cr] and protein concentrations ([P]) were analyzed in 631 spot urine samples with negative/equivocal dipstick from 425 pregnant women. False-negative dipstick was defined as [P] : [Cr] ratio (P/Cr) > 0.27 mg/mg.
Results: Median [Cr] was 117 mg/dL (range, 6.5-326 mg/dL), 72 mg/dL (range, 4.3-477 mg/dL), and 73 mg/dL (range, 8.4-396 mg/dL) in the first (n = 96), second (n = 344), and third (n = 191) trimester urine samples, respectively (P = 0.000, Kruskal-Wallis). Both [P] and P/Cr increased significantly with advancing gestation. FNR 9.4% (18/191) in the third trimester was significantly higher than that of 0.0% (0/96) in the second trimester and that of 0.5% (2/344) in the third trimester. In the 20 urine samples with false-negative dipstick, median [Cr] was 47.0 mg/dL (range, 11.0-358 mg/dL) and the proportion of samples with dilute urine, that is, [Cr] <47 mg/dL, was significantly higher than in the remaining 611 urine samples (50%, 10/20 vs 28%, 174/611, respectively, P = 0.046).
Conclusions: Urine samples in the second and third trimesters were more likely to be diluted compared with the first trimester. This was associated with high FNR in third trimester urine samples.
Keywords: pre-eclampsia; proteinuria pregnancy; protein : creatinine ratio; urine dipstick.
© 2017 Japan Society of Obstetrics and Gynecology.