1 hour Oral Glucose Tolerance Test, OGTT, GTT , one hour oral glucose challenge test,
GCT (serum, plasma)| Units | Fasting | 1 hour | ||
| mg/dL | Not required | 130 or 140 | ||
| mmol/L | Not required | 7.2 or 7.8 |
The one hour oral glucose challenge test [GCT]
is a screening test for gestational diabetes that measures plasma or serum glucose concentration 1 hour after a 50-g oral glucose load. A
blood sugar value >140 mg/dl (7.8 mmol/l) identifies approximately 80% of
women with gestational diabetes (GDM), a cutoff of >130 mg/dl (7.2 mmol/l) identifies 90% of
women with GDM.
The California Diabetes and Pregnancy Program
recommends that women with values 140 mg/dl to 179 mg/dl should have a 3-hour 100 gram oral
glucose tolerance test (OGTT) within one week. If the patient has a screening value > 180 mg/dl, a fasting blood sugar should
be checked as soon as possible. If the fasting is > 95 and the one hour
screening test > 180 mg/dl this provides two abnormal values and the 3 hour OGTT
is not required.
If the fasting value is less than 95 then proceed with the 3 hour OGTT.
A glucose challenge test is not necessary in patients with a fasting plasma glucose level >126 mg/dl (7.0 mmol/l) or a casual plasma glucose >200 mg/dl (11.1 mmol/l) since these values meet the threshold for the diagnosis of diabetes.
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