The 50g glucose challenge test does not diagnose gestational diabetes

Taking a blood test during pregnancy

This systematic review found that the 50g test is not accurate enough to diagnose gestational diabetes on its own.

Clinical question

In pregnant women <32 weeks gestation, what is the sensitivity and specificity of the 50g glucose challenge test?

The conventional test for diabetes is the oral glucose tolerance test (OGTT), in which a woman has to fast for several hours before being given an oral glucose solution.  Her blood is then sampled at intervals to see how well her body metabolises the additional sugar.

The 50g glucose challenge test is a simpler test in which the woman does not have to fast and only has one blood sample taken, one hour after drinking 50g of glucose in solution.

The review set out to work out how well the 50g test performs in clinical practice at detecting gestational diabetes.

  • Sensitivity is the proportion of people with the disorder who test positive.  A test with a high sensitivity has a low rate of false negatives.
  • Specificity is the proportion of people without the disorder who test negative.  A test with a high specificity rarely gives false positives.

The evidence

Twenty-six studies were found, comprising 13,564 women. In better quality studies (those with consecutive recruitment):

  1. sensitivity was 0.74 (95% CI 0.62-0.87)
  2. specificity was 0.85 (95% CI 0.80-0.91).

Neither value is high enough to consider the 50g test definitive for gestational diabetes.

Appraisal hints

Users of this research should consider:

  • Did the reviewers perform blind, independent evaluation of the individual studies?
  • Consider the quality of the individual studies.
  • Consider the population of the individual studies, and whether appropriate subgroup analysis revealed patterns in the performance of the test.
  • Although the review abstract claims that the 50g test may have a role in screening, its sensitivity of 0.74 means that one in four patients who test negative actually turn out to have gestational diabetes.
  • Although they looked for studies that compared the 50g test with the OGTT test, the review does not report a direct comparison in the abstract.  Readers need to evaluate this comparison to be able to

Reference

van Leeuwen M, Louwerse M, Opmeer B, Limpens J, Serlie M, Reitsma J, Mol B. Glucose challenge test for detecting gestational diabetes mellitus: a systematic review. BJOG 2012; DOI: 10.1111/j.1471-0528.2011.03254.x.

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Badenoch

Badenoch
I am an information scientist with an interest in making knowledge from systematic research more accessible to people who need it. This means you. I've been attempting this in the area of Evidence-Based Health Care since 1995. So far the results have been mixed. For some reason we expected busy clinicians to search databases and appraise papers instead of seeing patients. We also expected publishers to make the research freely available to the people who paid for it.. Ha! Hence The National Elf service.

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