Glucose challenge test

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:

A level of 7.8 mmol/L (or ≥ 8.0 mmol/L for 75g) has been suggested for Australia.

Patients with a glucose of 7.8 mmol/L or more (or ≥ 8.0 mmol/L for 75 g) should undergo formal glucose tolerance testing.

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.