Glucose challenge test
Last updated: Monday, 22, March, 2004
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| Item | Process |
|---|---|
| Specimen | The non-fasting patient drinks 50 g or 75 g glucose in a flavoured drink over ten minutes. One hour after commencing the drink, a specimen of blood is taken for plasma glucose. The preferred specimen is 5 mL blood in a fluoride oxalate tube. Collection in plain or lithium heparin tubes is satisfactory if the specimen is delivered promptly to the laboratory. |
| Method | Spectrophotometry. |
| Protocol | All pregnant women should be screened for gestational diabetes at 26-28 weeks. Patients at high risk for gestational diabetes (eg, previous large baby) should have a formal glucose tolerance test, rather than a glucose challenge test. |
| Reference Interval | The cutoff is taken at the eighty-fifth centile. This may vary with the population. A level of 7.8 (50 g test) or 8.0 mmol/L (75 g test) has been suggested for Australia. |
| Application | To identify the women most at risk of developing gestational diabetes mellitus. |
| Interpretation | If absorption of glucose from the gut is normal, women with a level below the cutoff have a low risk of gestational diabetes; whereas those at or above the cutoff are at higher risk, and should have an oral glucose tolerance test for definitive diagnosis. |
| Reference | Rumbold |