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Diagnosis of Diabetes

Oral Glucose Tolerance Test (OGTT) continued...

Table 2. Oral Glucose Tolerance Test

2-Hour Plasma Glucose Result (mg/dL) Diagnosis
139 and below Normal
140 to 199 Prediabetes
(impaired glucose tolerance)
200 and above Diabetes*

*Confirmed by repeating the test on a different day.

Gestational diabetes is also diagnosed based on plasma glucose values measured during the OGTT. Blood sugar levels are checked four times during the test. If your blood sugar levels are above normal at least twice during the test, you have gestational diabetes. Table 3 shows the above-normal results for the OGTT for gestational diabetes.

Table 3. Gestational Diabetes: Above-Normal Results for the Oral Glucose Tolerance Test

When Plasma Glucose Result (mg/dL)
Fasting 95 or higher
At 1 hour 180 or higher
At 2 hours 155 or higher
At 3 hours 140 or higher

Note: Some laboratories use other numbers for this test.

For additional information about the diagnosis and treatment of gestational diabetes, see the NIDDK booklet What I Need to Know About Gestational Diabetes.

Random Plasma Glucose Test

A random blood glucose level of 200 mg/dL or more, plus presence of the following symptoms, can mean that you have diabetes:

  • Increased urination
  • Increased thirst
  • Unexplained weight loss

Other symptoms include fatigue, blurred vision, increased hunger, and sores that do not heal. Your doctor will check your blood glucose level on another day using the FPG or the OGTT to confirm the diagnosis of diabetes.

Newer guidelines use hemoglobin A1c as a screening tool for prediabetes or diabetes (the test is normally used to measure blood glucose control in diabetes patients over several months). An HbA1c of 5.7% to 6.4% is consistent with prediabetes and marks a time when it can be reversed by lifestyle changes. An HbA1c of 6.5% or higher is consistent with diabetes.

WebMD Medical Reference

Reviewed by Michael Dansinger, MD on October 07, 2014
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