Urine protein dipstick measurements. A screen for a standard, 24-hour urine collection

To determine if the sum of urine protein dipstick values recorded during every void can be used to screen for patients who need a standard, 24-hour urine collection for determination of protein excretion.

Thirty inpatient and 17 outpatient pregnant women undergoing 24-hour urine collection for protein concentration were enrolled. The volume, dipstick protein values and time of void were recorded. The 24-hour quantitative analysis of protein excretion performed by the laboratory was compared to the 24-hour sum of the products of each voided volume and dipstick value (dipstick factor).

The dipstick factor significantly correlated with the total 24-hour protein excretion (correlation coefficient 0.84, P < 1 x 10(-7)). A dipstick factor of > or = 300 mg, indicated proteinuria with a sensitivity of 96%, specificity of 90%, positive predictive value of 92% and negative predictive value of 95%. Separately, we found differences in the amount of protein excretion when the 24-hour period was divided into six 4-hour periods, using analysis of variance. Paired t test analysis of the mean protein excretion from 16:00 to 04:00 showed significantly higher results than did the protein excretion from 04:01 to 16:00 (1,197 +/- 356 mg vs. 674 +/- 158 mg, P < .0001).

The sum of dipstick factors in a 24-hour period is a reliable screening test for identifying patients who need the standard laboratory test for proteinuria.