OGTT Result Interpreter
OGTT Result Interpreter
Classify a standard 75 g oral glucose tolerance test in a non-pregnant adult. WHO and the ADA agree on the diabetes and impaired-glucose-tolerance cut-offs and genuinely disagree on impaired fasting glucose — 6.1 against 5.6 mmol/L — so the page asks which criteria you want rather than choosing one silently, because that single difference reclassifies two to five times as many people.
OGTT classification
Fasting + 2-hour → classificationFasting 5.9 mmol/L, 2-hour 6.5 mmol/L, WHO 2006 criteria
The two frameworks side by side
Impaired glucose tolerance — 2-hour 7.8 to 11.0 mmol/L (140 to 199 mg/dL) with fasting < 7.0 WHO and ADA agree
Impaired fasting glucose — WHO 6.1 to 6.9 mmol/L (110 to 125 mg/dL) · ADA 5.6 to 6.9 mmol/L (100 to 125 mg/dL)
- the load
- 75 g of anhydrous glucose dissolved in 250 to 300 mL of water, drunk over about five minutes, after an overnight fast of at least eight hours and at least three days of unrestricted carbohydrate. Timing runs from the first sip
- the sample
- venous plasma. A capillary meter is not a diagnostic sample. An uncentrifuged tube loses glucose to glycolysis at roughly 5 to 7% an hour, so a delayed sample reads falsely low unless the tube contains a glycolysis inhibitor
- if the 2-hour sample is missing
- the WHO report is explicit: “If 2-h plasma glucose is not measured, status is uncertain as diabetes or IGT cannot be excluded.” A fasting value alone cannot classify anybody, which is the part most often dropped
- one test is not a diagnosis
- without unequivocal hyperglycaemia, the ADA requires two abnormal results — two different tests on one sample, or the same test repeated. A single borderline value is repeated, not acted on
- HbA1c is a third framework
- the ADA adds HbA1c ≥ 6.5% (48 mmol/mol) for diabetes and 5.7 to 6.4% (39 to 47 mmol/mol) for prediabetes. It is measured on a different sample over a different time window and routinely disagrees with the OGTT in both directions
Worked example
Fasting 5.9 mmol/L, 2-hour 6.5 mmol/L, WHO 2006 criteria
Fasting 5.9 is below WHO's impaired-fasting-glucose threshold of 6.1 mmol/L
2-hour 6.5 is below the impaired-glucose-tolerance threshold of 7.8 mmol/L
So on WHO criteria this is normal glucose tolerance
Now switch the selector to the ADA. Nothing about the patient changes
The ADA's impaired-fasting-glucose range starts at 5.6 mmol/L (100 mg/dL), and 5.9 is inside it
The same two numbers now read impaired fasting glucose — prediabetes
This is not a rounding artefact. It is the single largest disagreement in glucose diagnostics, and it is why this page makes you pick
Where WHO and the ADA agree, and where they do not
| Category | WHO 2006 / IDF | ADA Standards of Care | Agree? |
|---|---|---|---|
| Diabetes — fasting | ≥ 7.0 mmol/L (126 mg/dL) | ≥ 7.0 mmol/L (126 mg/dL) | Yes |
| Diabetes — 2-hour | ≥ 11.1 mmol/L (200 mg/dL) | ≥ 11.1 mmol/L (200 mg/dL) | Yes |
| Impaired glucose tolerance — 2-hour | 7.8 to 11.0 mmol/L (140 to 199 mg/dL) | 7.8 to 11.0 mmol/L (140 to 199 mg/dL) | Yes |
| Impaired fasting glucose — fasting | 6.1 to 6.9 mmol/L (110 to 125 mg/dL) | 5.6 to 6.9 mmol/L (100 to 125 mg/dL) | No |
| HbA1c — diabetes | ≥ 6.5% (48 mmol/mol) | ≥ 6.5% (48 mmol/mol) | Yes |
| HbA1c — intermediate | WHO does not define a range | 5.7 to 6.4% (39 to 47 mmol/mol) | No |
How much the fasting cut-point moves
| Population | IFG prevalence at 6.1 mmol/L (WHO) | IFG prevalence at 5.6 mmol/L (ADA) |
|---|---|---|
| United States | 6.7% | 24.1% |
| Denmark | 11.8% | 37.6% |
| France | 15.9% | 45.2% |
The same patient, both ways
| Fasting | 2-hour | WHO 2006 | ADA |
|---|---|---|---|
| 5.4 mmol/L (97 mg/dL) | 6.2 mmol/L (112 mg/dL) | Normal | Normal |
| 5.9 mmol/L (106 mg/dL) | 6.5 mmol/L (117 mg/dL) | Normal | Impaired fasting glucose |
| 6.4 mmol/L (115 mg/dL) | 7.1 mmol/L (128 mg/dL) | Impaired fasting glucose | Impaired fasting glucose |
| 5.5 mmol/L (99 mg/dL) | 9.2 mmol/L (166 mg/dL) | Impaired glucose tolerance | Impaired glucose tolerance |
| 6.5 mmol/L (117 mg/dL) | 9.8 mmol/L (177 mg/dL) | IFG and IGT | IFG and IGT |
| 7.3 mmol/L (132 mg/dL) | 9.0 mmol/L (162 mg/dL) | Diabetes | Diabetes |
| 5.2 mmol/L (94 mg/dL) | 11.6 mmol/L (209 mg/dL) | Diabetes | Diabetes |
One test, two frameworks, and one real disagreement
The 75 g oral glucose tolerance test is the oldest of the diabetes diagnostics and still the most informative, because it is the only one that sees what happens to glucose under a load. A fasting sample reports hepatic glucose output in the basal state; an HbA1c reports average exposure over months; the 2-hour value reports how well the pancreas and the peripheral tissues cope with 75 g of glucose arriving at once. Those are three different physiological questions, which is why the three tests routinely disagree in the same person and why none of them is a substitute for the others.
On the two thresholds that define diabetes, the World Health Organization and the American Diabetes Association agree exactly: a fasting plasma glucose of 7.0 mmol/L (126 mg/dL) or above, or a 2-hour value of 11.1 mmol/L (200 mg/dL) or above. They agree equally on impaired glucose tolerance, which is a 2-hour value of 7.8 to 11.0 mmol/L (140 to 199 mg/dL) with a fasting value below 7.0. Where they part company is the lower boundary of impaired fasting glucose. WHO puts it at 6.1 mmol/L (110 mg/dL); the ADA lowered it to 5.6 mmol/L (100 mg/dL) in 2003 and WHO’s own consultation, reviewing the same evidence in 2005, concluded that its cut-point should not be changed.
That gap of half a millimole is not a technicality. The European Diabetes Epidemiology Group calculated what it does to the size of the affected population: impaired fasting glucose prevalence rises from 6.7% to 24.1% in the United States, from 11.8% to 37.6% in Denmark and from 15.9% to 45.2% in France — a two- to five-fold increase worldwide. Its objections were specific. The association with incident diabetes is weaker in the newly captured 5.6 to 6.0 band than in the 6.1 to 6.9 band; the extra group adds nothing to cardiovascular risk prediction; and there is no trial showing that lifestyle or drug intervention helps people in that band, because the prevention trials recruited on impaired glucose tolerance, not on the lowered fasting threshold. The counter-argument is equally coherent: risk is continuous, earlier identification allows earlier intervention, and a label that prompts a conversation about weight and activity does little harm. This page does not adjudicate. It reports which framework produced your answer, and shows you the other one.
Two practical points decide whether the result means anything at all. The sample must be venous plasma, taken into a tube that stops glycolysis or separated promptly — glucose falls by roughly 5 to 7% an hour in an uncentrifuged tube, which is enough to turn a diagnosis into a normal result. And the 2-hour sample must actually be taken. The WHO report is blunt about the alternative: if the 2-hour plasma glucose is not measured, “status is uncertain as diabetes or IGT cannot be excluded”. A fasting value on its own cannot classify anyone, and the last row of the table above shows why — a fasting glucose of 5.2 mmol/L with a 2-hour value of 11.6 is diabetes, and a fasting-only strategy calls that person healthy. If you need to move between units, the glucose unit converter carries the diagnostic thresholds in both.
Frequently asked questions
What is a normal 2-hour OGTT result?
Below 7.8 mmol/L (140 mg/dL). WHO and the ADA use the same figure. A 2-hour value of 7.8 to 11.0 mmol/L (140 to 199 mg/dL) is impaired glucose tolerance and 11.1 mmol/L (200 mg/dL) or above meets the diabetes threshold. The fasting value has to be interpreted alongside it, and that is where the two bodies differ.
Why do WHO and the ADA disagree about impaired fasting glucose?
The ADA lowered its lower cut-point to 5.6 mmol/L (100 mg/dL) in 2003 to capture more people at risk. WHO reviewed the same question in 2005 and kept 6.1 mmol/L (110 mg/dL), on the grounds that the extra band predicts diabetes less strongly, adds nothing to cardiovascular risk prediction, and has no intervention trial behind it. Both positions are deliberate.
How many more people are labelled if the threshold is 5.6 rather than 6.1?
Between two and five times as many. The European Diabetes Epidemiology Group put United States prevalence at 6.7% versus 24.1%, Denmark at 11.8% versus 37.6% and France at 15.9% versus 45.2%. In France that is the difference between one adult in six and nearly one in two.
Can diabetes be diagnosed from a single OGTT?
Not usually. Without unequivocal hyperglycaemia the ADA requires two abnormal results — either two different tests on the same sample or the same test repeated on a second sample. Where symptoms of hyperglycaemia accompany a clearly diagnostic value, treat rather than wait for confirmation.
Is the fasting glucose enough, or does the 2-hour sample matter?
The 2-hour sample matters. WHO states that without it, status is uncertain because neither diabetes nor impaired glucose tolerance can be excluded. Isolated impaired glucose tolerance — a normal fasting glucose with an abnormal 2-hour value — is invisible to fasting glucose and often to HbA1c as well, and it is a strong predictor of cardiovascular mortality.
Does this page apply in pregnancy?
No. Pregnancy uses lower thresholds and a different framework entirely, and reading a pregnancy OGTT against these criteria would miss most gestational diabetes. Use the gestational diabetes OGTT interpreter instead.
Related calculators
References
- World Health Organization, International Diabetes Federation. Definition and diagnosis of diabetes mellitus and intermediate hyperglycaemia: report of a WHO/IDF consultation. Geneva: WHO; 2006.
- American Diabetes Association Professional Practice Committee. 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes—2025. Diabetes Care. 2025;48(Suppl 1):S27–S49.
- Forouhi NG, Balkau B, Borch-Johnsen K, et al; EDEG. The threshold for diagnosing impaired fasting glucose: a position statement by the European Diabetes Epidemiology Group. Diabetologia. 2006;49(5):822–827.
- World Health Organization. Use of glycated haemoglobin (HbA1c) in the diagnosis of diabetes mellitus: abbreviated report of a WHO consultation. Geneva: WHO; 2011.
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