Withstanding the test of time: Morning versus afternoon/evening urine protein-to-creatinine ratios in preeclampsia.

Objective: There are mixed findings regarding time preference for measuring spot urine protein to creatinine ratios (UPCR) in renal patients but no such literature among pregnant patients. We compare AM versus PM measurements for UPCR among pregnant patients with preeclampsia.

Study Design: This retrospective study included 163 patients diagnosed with preeclampsia. Laboratory tests of UPCR, urine specificity gravity, and uric acid were collected for these patients during the morning (AM) 12:00 AM (00:00) through 11:59 AM (11:59) and afternoon/evening (PM) 12:00 PM (12:00) through 11:59 PM (23:59).

Main Outcome Measures: Outcomes were UPCR percentages indicative of preeclampsia, UPCR median values, abnormal uric acid, and normal urine specific gravity indicative of a quality sample for measuring UPCR.

Results: UPCR ≥ 0.3 indicative of preeclampsia significantly differed (p < 0.001) where the AM group (76.7 %) had a greater percentage than the PM group (52.8 %). Median UPCR significantly differed (p < 0.001) where the AM group had a greater median (0.44) than the PM group (0.32). None of the uric acid or urine specific gravity comparisons significantly differed between the AM and PM groups. Similar patterns occurred for subgroups of those with hypertension, nulliparous, and preeclampsia with severe features.

Conclusion: We found that UPCR had greater median values and more values indicative of preeclampsia for AM measurements than PM measurements. Clinicians who use spot urine measurements and not 24-hour urine measurements should preferably measure UPCR in the AM rather than the PM.