Finding the right tests…
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Finding the right tests…
Glucose
GTT Fasting is the first blood sample drawn when your doctor orders a full glucose tolerance test — taken before you drink the glucose solution, not as a stand-alone check. It captures your baseline sugar level so the lab can compare it against the readings taken after the drink, usually at one, two, or three hours. On its own this number looks identical to an ordinary fasting glucose test, but its purpose here is different: it is the starting point of a curve, not a final answer, and your doctor reads it alongside the later samples rather than by itself.
This sample reports your plasma glucose in mg/dL at the exact moment before the glucose drink is given, using the same laboratory method as any other blood glucose sample. What sets it apart is how it's used: the lab pairs this fasting figure with each later timed sample from the same test session to build a glucose curve, so your doctor can see not just one number but the whole pattern of rise and fall across the hours that follow.
A glucose tolerance test is really a series of measurements, and this fasting draw is the anchor point for all of them. After this first sample, you drink a measured glucose solution — the amount depends on which protocol your doctor has chosen, commonly 75 grams for a general diabetes or one-step gestational diabetes check, or 100 grams for the older two-step gestational diabetes protocol — and further samples are drawn at set intervals afterward.
Even though it's part of a bigger test, this fasting value carries real weight. In the widely used two-step gestational diabetes protocol, a fasting reading of 95 mg/dL or higher is one of four values checked, and two or more abnormal values out of the four confirm the diagnosis. In the one-step 75-gram protocol, a single abnormal value — including this fasting one, at 92 mg/dL or higher — is enough to confirm gestational diabetes.
Once this sample is drawn, you'll be given the glucose drink and asked to wait without eating, drinking anything else, or moving around too much, since activity can affect how your blood sugar responds over the following hours.
The blood draw itself is identical, but the purpose is different. A stand-alone fasting test is read on its own, while this fasting sample is the baseline for a full glucose tolerance series and is interpreted together with the later timed samples.
Guidance for a glucose tolerance test generally calls for 8 to 14 hours of fasting beforehand. Follow whatever specific instruction your own doctor has given you for the protocol they've ordered.
You'll drink a glucose solution and then wait for further blood samples at set times. These are often taken once every hour for the next two or three hours, depending on which protocol your doctor has ordered.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
It's the baseline every later sample gets compared against. In the Carpenter-Coustan protocol, a fasting value of 95 mg/dL or higher counts as one of four checked values, and two abnormal values out of four confirm gestational diabetes.
That depends on the medicine, so check with your doctor beforehand. Don't stop or delay a prescribed medicine on your own just because a fasting test is scheduled.
Feeling light-headed after drinking the glucose solution is a recognised side effect of the test. It's a good idea to have someone available to accompany you home afterward.
No. The same fasting-plus-timed-draw structure is used to confirm prediabetes or type 2 diabetes in anyone, not only pregnant women, though the glucose dose and number of follow-up draws differ by protocol.