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 AR and Crowther CA. Aust N Z J Obstet Gynaecol. 2001; 41(1): 86-90.