Glucose Challenge Test (GCT): Introduction, Procedure, Result-Interpretation, and Keynotes

Introduction of Glucose Challenge Test

The glucose challenge test (GCT) measures the body’s response to glucose (sugar) and it is tested during pregnancy to screen for gestational diabetes (diabetes that develops during pregnancy). The GCT is done in two steps. Initially drink a glass of water with sugar i.e. sugary solution. An hour later, the blood sugar level is measured.

Test Requirements

• 50 gm glucose
• Glass
• Water
• Blood sample

Procedure of GCT

The GCT is done in two steps. The health care provider’s office/lab will provide 50 gm of sugar and a glass with water having nearly 150 ml of water that you have to drink and wait for an hour. Just after the completion of an hour, a blood sample will be taken from a vein in your arm. This blood specimen will be used to measure your blood sugar level. After the GCT, you can return to your usual activities immediately.

Result-Interpretation of Glucose Challenge Test

• Normal range: <140 mg/dL (7.8 mmol/L)
• In doubtful gestational diabetes: 140 mg/dL (7.8 mmol/L) to 189 mg/dL-In this case, there is a need for a three-hour GTT to diagnose gestational diabetes.
• In gestational diabetes: ≥190 mg/dL (10.6 mmol/L)

Keynotes on GCT

1. If the value of the test result is above normal, there is a need for further testing to determine the diagnosis.
2. The GCT is generally tested between weeks 24 and 28 of pregnancy.
3. GCT assay is also useful as early as the first prenatal visit if the pregnant lady is at high risk of gestational diabetes due to obesity, a personal history of gestational diabetes, a family history of diabetes, or other factors.
4. Most pregnant women having gestational diabetes deliver healthy babies. Although without careful management, gestational diabetes can create multiple pregnancy complications, like excess fetal growth that might increase the risk of birth injuries or prompt a cesarean section delivery.
5. Eating and drinking are not avoided before the GCT.
6. Women of race and ethnicities like Black, Hispanic, American Indian, and Asian American are at higher risk of developing gestational diabetes.
7. Results of GCT are expressed in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L).
8. Some laboratories use a lower threshold of 130 mg/dL (7.2 mmol/L) when screening for gestational diabetes.
9. The American College of Obstetricians and Gynecologists also recommends that women diagnosed with gestational diabetes have a two-hour glucose tolerance test (GTT) 4 to 12 weeks after childbirth which is useful to screen for type 2 diabetes.