In a 1-hour glucose challenge test with 50 g glucose, when is the test considered positive?

• A. Greater than 130 mg/dL
• B. Greater than 110 mg/dL
• C. Greater than 150 mg/dL
• D. Greater than 100 mg/dL

Answer: (A)

Think of the 1-hour glucose challenge test as a screening step for gestational diabetes. After giving a 50-gram glucose load, you measure the blood glucose at one hour. If that value is above the commonly used cutoff, the screen is positive and the patient should proceed to the diagnostic test (the fasting 3-hour 100-gram oral glucose tolerance test).

The threshold used for a positive screen is about 130 mg/dL. Choosing 130 mg/dL helps catch more women who may have gestational diabetes, prompting the follow-up diagnostic test. If the result is lower, the screen is considered negative and no immediate further testing is required unless other risk factors exist. Some guidelines vary and may use 140 mg/dL, which is why 130 mg/dL is the answer here.

After a positive screen, the next step is the comprehensive diagnostic test, where two or more values among fasting, 1-hour, 2-hour, and 3-hour measurements each have specific cutoffs to confirm or rule out gestational diabetes.