Blood glucose curve: what it is, when it is important and why this test is performed

By Cristiano Antonino On Feb 21, 2023

The glycaemic curve (or rather oral glucose load curve, also known by its acronym OGTT) is a test used to diagnose diabetes mellitus

The test measures blood glucose values with a blood sample taken on an empty stomach and two hours after taking an oral glucose solution.

The blood glucose curve test is also used in pregnancy to screen for gestational diabetes, in which case three samples are taken (fasting, after one hour and two hours after taking the glucose solution).

What is the blood glucose curve?

The blood glucose curve makes it possible to detect changes in carbohydrate metabolism.

In particular, blood glucose values that are below 140 mg/dl after two hours are considered normal.

For values between 140 and 200 mg/dl the alteration is identified as ‘reduced carbohydrate tolerance’ (a pre-diabetes condition) and for values above 200 mg/dl the diagnosis of diabetes mellitus can be made.

For gestational diabetes, on the other hand, the parameters are different. Values below 92 mg/dl on an empty stomach, below 180 mg/dl at 1 hour and below 153 mg/dl at 2 hours indicate a normal condition.

Even a single value above these limits makes it possible to diagnose gestational diabetes, a condition that it is important to keep under control for the health of the mother and the unborn child.

Blood glucose curve, are there any rules for preparing for the test?

The test is performed early in the morning, on an empty stomach.

Which patients can have a blood glucose test?

Patients with an impaired fasting blood glucose value, i.e. fasting values above 100 mg/dl but below 126 mg/dl, may be asked to have a blood glucose curve performed.

The fasting blood glucose value considered normal is below 100 mg/dl.

Two fasting blood glucose values above 126 mg/dl, or a single value at any time of the day above 200 mg/dl, or a glycated haemoglobin value above 6.5 per cent already allow the diagnosis of diabetes mellitus.

Pregnant women with risk factors for the development of gestational diabetes may also take the test, on the advice of their gynaecologist.