OGTT Oral glucose load test

OGTT is the acronym for Oral Glucose Tolerance Test, an Anglo-Saxon term Italianized in Glucose oral load test.

OGTT indications

The test is performed for the diagnosis and screening of diabetes mellitus and glucose intolerance (IGT). This last condition is considered a pre-diabetic state, with a risk of evolution into overt diabetes in the years to come. The OGTT is performed, with due care, also for the diagnosis and screening of gestational diabetes and to monitor the repercussions glycemic disorders of polycystic ovary syndrome.

OGTT measures the ability of the body's cells to use glucose by taking it from the blood; glucose, or dextrose, is the sugar that represents the main energy source of our body.

OGTT contraindications

The test is contraindicated if fasting glycaemia exceeds 126 mg / dl, a condition in itself sufficient to diagnose diabetes. The same applies if random glycemic values ​​higher than 200 mg / dl are detected.

Preparation for the OGTT exam

Present yourself for the exam on an absolute fast (only water is allowed) for at least 8 hours, without exceeding 14 hours. In the days preceding the test, follow a normally balanced diet, without excess calories or particular precautions (obviously alcohol should be avoided); an intake of at least 150/200 grams of carbohydrates per day is recommended. Avoid strenuous physical exertion in the two or three days prior to the test.

The preventive suspension of any drugs interfering with glucose metabolism (such as steroids) is also very important, according to the advice of your doctor who must be warned in time for the examination (at least a few weeks).

OGTT execution

The examination takes place in the morning. The nurse carries out a blood glucose sample (fasting), then - if the measured value is less than 126 mg / dl - 75g of glucose dissolved in 250-300 ml of water are taken. "water, possibly in a short period of time. In the following hours the patient is asked to remain seated, without smoking or eating, possibly relaxed (emotional stress can distort the results). Blood glucose is measured at regular intervals, usually after 30, 60, 90 and 120 minutes from the ingestion of the first sip of glucose.

OGTT side effects

Nausea and vomiting, especially in pregnancy.

The examination is not painful; the blood samples are taken as in any other normal blood test, so you may feel a sting or a tingle at the time of collection. In subjects with coagulation problems it may be difficult to stop the baby. post-sampling haemorrhage The whole blood volume withdrawn is limited, so normally there are no problems (such as anemia) in this sense.

The aqueous glucose solution has a very sweet taste.

OGTT interpretation

If after 120 minutes the glycaemia is between 140 and 199 mg / dl, a diagnosis of glucose intolerance is made.
If blood glucose is ≥ 200mg / dl after 120 minutes, diabetes mellitus is diagnosed.

Glycemic levels Normal

Altered blood sugar a
fasting (IFG)

Altered tolerance
glucose (IGT)

Diabetes mellitus


Venous plasma Fast 120' Fast 120' Fast 120' Fast 120' (mg / dl) <110 <140 > 110* - <126 <140 <126 >140 < 200 >126 >200 (mmol / l) <6.1 <7.8 > 6.1 - <7.0 <7.8 <7.0 >7.8 >7.0 >11.1

1999 WHO Diabetes criteria - Interpretation of Oral Glucose Tolerance Test - OGTT

* > (100 mg / dl according to the ADA)

NOTES: the finding of glycaemia higher than 200 mg / dL after two hours of glucose load indicates (if confirmed a second time) the presence of diabetes mellitus even if the fasting glycaemia is less than 126 mg / dL.

Impaired glucose tolerance is a condition to be monitored constantly, both for the possible evolution to diabetes mellitus, and for the greater cardiovascular risk compared to people with normoglycemia. The same applies in the presence of impaired fasting glycaemia, a condition in itself less worrying than to the previous one.

OGTT variants

In pregnancy, for the research of gestational diabetes, the oral mini-load with 50g of glucose (GCT) and the OGTT with 100g of glucose are used.

none:  urinary-tract-health doping martial arts