- Screening for gestational diabetes using urine dipsticks for glycosuria is ineffective with low sensitivities. False-positive tests outnumber true positives 11:1. A 50-g oral glucose challenge is a better test. Tests for glycosuria after this blood test are not useful (B).
- Proteinuria determined by dipstick in pregnancy is common and a poor predictor for preeclampsia with a positive predictive value between 2% and 11%. If the blood pressure is elevated, a more sensitive test should be used (B).
- After urinalysis at the first prenatal visit, routine urine dipstick screening should be stopped in low-risk women (B).
- Objective: More than 22 million prenatal visits occur in the US each year.1 Each pregnant woman averages 7 visits. Most include urine testing for glucose and protein to screen for gestational diabetes and preeclampsia. Is there sufficient scientific evidence to support this routine practice?
- Methods: We searched Medline (1966–2004), the Cochrane review, AHRQ National Guideline Clearinghouse, the Institute for Clinical Systems Improvement, and Google, searching for studies on proteinuria or glycosuria in pregnancy. The reference list of each article reviewed was examined for additional studies, but none were identified. We found 6 studies investigating glycosuria as a predictor for gestational diabetes mellitus, or proteinuria as a predictor for preeclampsia (1 examined both). Because every study used different dipstick methods of determining results, or definitions of abnormal, each was evaluated separately.
- Results: Glycosuria is found at some point in about 50% of pregnant women; it is believed to be due to an increased glomerular filtration rate.3 The renal threshold for glucose is highly variable and may lead to a positive test result for glycosuria despite normal blood sugar. High intake of ascorbic acid or high urinary ketone levels may result in false-positive results. Four published studies assessed the value of glycosuria as a screen for gestational diabetes.4-7 All used urine dipsticks. Three of the 4 most likely overestimate the sensitivity of glycosuria for predicting gestational diabetes.
- Conclusions: Routine dipstick screening for protein and glucose at each prenatal visit should be abandoned. Women who are known or perceived to be at high risk for gestational diabetes or preeclampsia should continue to be monitored closely at the discretion of their clinician.
Routine dipstick testing is time-consuming and expensive, especially when carried out over multiple visits. False-positive test results are frequent and often lead to further laboratory examinations. Today, when our care of patients is squeezed by both time and monetary constraints, we have a rare opportunity to make office visits more productive and to save patients the burden of unnecessary work-ups.
We searched Medline from 1966 to September 2004 for English language articles using keyword searching for “proteinuria” or “glycosuria” and “prenatal” or “pregnancy.” We explored the Cochrane review, AHRQ National Guideline Clearinghouse, the Institute for Clinical Systems Improvement, and Google. The reference list of each article reviewed was examined for additional studies, but none were identified.
All 6 identified studies that investigated glycosuria as a predictor for gestational diabetes mellitus or proteinuria as a predictor for preeclampsia are reviewed in this analysis. One study examined both. Because every study used different dipstick methods of determining results, or definitions of abnormal, each was evaluated separately.
What the evidence shows
Found at some point in about 50% of women, glycosuria is believed to be due to an increased glomerular filtration rate.3 The renal threshold for glucose is highly variable and may lead to a positive test result for glycosuria despite a normal blood sugar. High intake of ascorbic acid or high urinary ketone levels may result in false-positive results. There have been 4 published studies designed to assess the value of glycosuria as a screen for gestational diabetes mellitus.4-7 All used urine dipsticks (TABLE 1).
Watson: Urine test a poor screening instrument
In an observational prospective study of 500 women, Watson evaluated glycosuria (trace, ≥100 mg/dL) detected on 2 separate prenatal visits (17% of women) as a predictor of gestational diabetes.4 Gestational diabetes was defined as an abnormal 50-g glucose screen at 28 weeks gestation confirmed by an abnormal 100-mg 3-hour oral glucose tolerance test (OGTT).
He reported that glycosuria used as a screening test for gestational diabetes had a sensitivity of 27% and a specificity of 83% with a negative predictive value (PV–) of 96% and a positive predictive value (PV+) of 7% in a population with an unusually high prevalence of gestational diabetes of 4.4%. The high prevalence of gestational diabetes in this cohort increased the PV+ of urine screening for glycosuria. Women with severe glycosuria (>250 mg/dL, 2+) on 2 determinations during the first 2 trimesters had a 21% chance (PV+) of being diagnosed as having gestational diabetes.