How does a 12-hour vs 24-hour Urine Collection Compare When Evaluating Preeclampsia?
BACKGROUND AND PURPOSE:
ACOG guidelines provide the following proteinuria criteria
24-hour urine collection > 300 mg protein or single voided urine protein/creatinine ratio > 0.3 mg/dl
Silva et al. (International Journal of Gynecology & Obstetrics, 2018) assessed the accuracy of a 12-hour urine collection compared to 24-hour, including whether diurnal vs nocturnal collection affected test performance
Prospective observational study
Participants: Women being assessed for preeclampsia ≥20 weeks
Two consecutive urine samples were collected at
Protein levels were measured in each 12‐hour sample
The two 12-hour samples were then mixed and homogenized with final quantification of the overall 24-hour pooled sample (07:00–07:00 hours)
Diagnostic cut‐off values
150 mg (12‐hour sample)
300 mg (24‐hour sample)
Detection of preeclampsia
Equivalence of diurnal and nocturnal proteinuria values
Multiple measurements were available from the participants
Power calculation was conducted, demonstrating 372 measurements were necessary to establish non-inferiority of the 12-hour method
99 patients were involved in the study
456 12‐hour urine samples were analyzed (equivalent to 228 24‐hour samples)
Reliability and validity analysis
12-hour sample vs 24-hour: Substantial level of agreement (Cohen κ 0.779)
Diurnal vs 24-hour: Substantial level of agreement (Cohen κ 0.719)
Nocturnal vs 24-hour: Almost perfect agreement (Cohen κ 0.838)
No statistically significant difference was found between the two 12‐hour collections
When compared to 24-hour collection, the 12-hour samples demonstrated
Sensitivity: 85.9% (95% CI, 81%–90%)
Specificity: 91.7% (95% CI, 88%–95%)
PPV: 88.2 (95% CI, 83.6–92.9)
NPV: 90 (95% CI, 86.4–93.6)
12-hour testing led to accurate detection of pre-eclampsia in women at risk and could be considered an alternative to the “gold standard” 24-hour test
Both 12 and 24-hour collections detected similar levels of proteinuria with a discrepancy of less than 10% (within a priori study parameters)
There was no observed circadian effect on urine samples
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