Impaired glucose tolerance (IGT)

Q: How does IGT differ from impaired fasting glucose?

In impaired fasting glucose it is specifically the fasting sugar that is elevated (5.6–6.9). In IGT the fasting value may be normal, but the sugar drops poorly after eating (7.8–11.0 at 2 hours). Both are prediabetes.

Q: Will IGT go away on its own?

Without changes, it more often progresses to diabetes. But it is the most favorable point for intervention: weight loss and activity return carbohydrate metabolism to normal in a significant proportion of people.

An intermediate state between normal and diabetes

Impaired glucose tolerance — the blood sugar curve after a load

IGT is a form of prediabetes: fasting blood sugar is still normal or slightly elevated, but it drops poorly after eating. It is an early manifestation of insulin resistance.

It is detected by a glucose tolerance test (75 g of glucose): a value of 7.8–11.0 mmol/L at 2 hours is already not normal, but not yet the diabetic threshold (11.1).

What it means

IGT shows that the body handles sugar worse than normal. This substantially increases the risk of type 2 diabetes mellitus and cardiovascular disease in the coming years.

How it is detected

Fasting glucose alone will not reveal IGT — an oral glucose tolerance test (OGTT) is needed: blood is drawn fasting and 2 hours after taking 75 g of glucose.

Can it be reversed

Yes. A change of lifestyle (weight loss, nutrition, activity) reduces the transition of IGT to diabetes by more than half — this is proven in the large DPP study.

Reference ranges

Assessment by glucose at 2 hours in a glucose tolerance test (with fasting glucose < 7.0 mmol/L):

Normal	< 7.8 mmol/L
Impaired tolerance (IGT)	7.8 – 11.0 mmol/L
Diabetes mellitus	≥ 11.1 mmol/L

Important: Impaired fasting glucose (fasting glucose 5.6–6.9 mmol/L) is distinguished separately — it is another form of prediabetes.

Calculate using this marker

Calculators where Impaired glucose tolerance (IGT) is used directly:

Diabetes Risk Screening for hidden prediabetes and type 2 diabetes from labs and risk factors Open METS-IR (Insulin Resistance) A non-insulin index of insulin resistance Open Metabolic Index An integrated assessment of your metabolic status Open

Frequently asked questions

How does IGT differ from impaired fasting glucose?

In impaired fasting glucose it is specifically the fasting sugar that is elevated (5.6–6.9). In IGT the fasting value may be normal, but the sugar drops poorly after eating (7.8–11.0 at 2 hours). Both are prediabetes.

Will IGT go away on its own?

Without changes, it more often progresses to diabetes. But it is the most favorable point for intervention: weight loss and activity return carbohydrate metabolism to normal in a significant proportion of people.

Sources

info

This content is educational and does not replace consultation with a physician. Reference ranges may vary depending on the laboratory and method — rely on the ranges stated on your own test report.

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