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Higher positive screen rate for gestational diabetes with fasting vs fed 1-hour glucose tolerance test
Question clinique
Do positive screen rates differ with fasting versus fed 1-hour glucose tolerance tests in second-trimester pregnancy?
L’Essentiel
The positive screen rate for the 1-hour 50-g oral glucose tolerance test was more than double among participants at greater than 24 weeks' gestation who had fasted for at least 6 hours compared with those who had eaten within 2 hours prior to testing. This study suggests, but doesn't prove, that prolonged fasting prior to 1-hour glucose tolerance testing leads to false positive results and unnecessary second-step testing. A larger study, powered to evaluate clinically meaningful differences in maternal and infant outcomes, is needed. 1b-
Référence
Plan de l'etude: Randomized controlled trial (nonblinded)
Financement: Self-funded or unfunded
Cadre: Outpatient (primary care)
Sommaire
The two-step method of oral glucose tolerance testing to screen for gestational diabetes in the second trimester of pregnancy is used nearly universally in the United States. These investigators conducted a randomized controlled trial to compare the positive screening rate for the first step in fasting versus fed conditions. They compared the results for participants who were instructed to fast for at least 6 hours before testing with the results for those who were instructed to eat normally within 2 hours prior to testing. The study included patients 18 years or older with a singleton pregnancy who were undergoing screening at 24 or more weeks' gestation. The authors excluded patients with pregestational diabetes, those given a diagnosis of diabetes in first trimester, those with an elevated 1-hour glucose tolerance test result before 24 weeks', those who used diabetes medication prior to pregnancy, those with daily oral steroid use for at least 4 weeks in the prior year, and those with history of bariatric surgery. A positive result was defined as glucose measurement of 140 mg/dL to 179 mg/dL 1 hour after a 50-g oral glucose load. Results of 180 mg/dL were considered diagnostic for gestational diabetes. Baseline characteristics were similar between groups, including age, body mass index, multiparity, and insurance type. Analysis was by intention to treat. The positive screen rate was 31/97 (32%) in the fasting group and 13/98 (13%) in the fed group (P = .002). There were no differences in maternal or neonatal outcomes between groups, though the study was not powered to detect them. The majority of participants expressed a preference of eating without restriction prior to testing (138/195 [71%]).
Reviewer
Linda Speer, MD
Professor and Chair, Department of Family Medicine
University of Toledo
Toledo, OH
Commentaires
Impact assessment
Excellent
Impact assessment
Excellent
conclusions drawn from article
"This study suggests, but doesn't prove, that prolonged fasting prior to 1-hour glucose tolerance testing leads to false positive results and unnecessary second-step testing"
I think that using the word "suggests" may be a bit too strong and potentially misleading. Yes, there were more positive results in the fasted group vs. the fed group (31 vs 13), and there were more false positives in the fasted vs. fed (19 vs. 8) with no differences in outcome.
However, the fasted group had more than double the cases of gestational diabetes than the fed group (12 vs. 5). Even though the number of cases of GDM was too small for this study to detect a significant difference (i.e. underpowered), the trend indicates that there was a difference in the groups' GDM rate (more than double) that was in line with the difference in the screen positive rate (also more than double). Useful additional information would be the number of false negatives (if any) for either group.
An alternative statement that captures more of the nuance demonstrated in the study: "This study shows a dramatic difference in screening outcomes based on whether patients have eaten or not before the 1-hour OGTT. This is a significant limitation in an otherwise very common pregnancy screening test. Unfortunately, this study did not have enough participants to draw conclusions on the rate of gestational diabetes among both groups. Therefore, it is impossible to draw a conclusion regarding how to advise patients on eating before the 1-hour OGTT." from https://www.practiceupdate.com/content/fasting-compared-with-fed-and-or…
Diabeti screening
Good to know
gestational diabetes
simple is best