Glucose tolerance curve

Results
NORMAL VALUES

Up to age 50: 60-115 mg/dl

What it means

• If the glucose value is lower than normal, so-called hypoglycaemia, the causes may be linked to a lifestyle that is not entirely healthy: poor diet, excessively long fasting, excessive muscular activity or alcohol abuse. Causes linked directly to the body, and so to possible diseases, include carbohydrate malabsorption, some enzyme deficiencies (glycogen storage disease) and tumours of the pancreas that produce too much insulin (a hormone that plays a key role in the metabolism of sugars and fats).
• If the glucose value is higher than normal, so-called hyperglycaemia, the main cause is diabetes (a lack of insulin). There are two types of diabetes:

1. Type 1 diabetes, insulin-dependent, once called “juvenile” diabetes, in which there is a lack of insulin that causes high blood glucose levels. This type of diabetes must be treated with insulin to avoid, in the long run, complications such as diseases of the eyes, kidneys, blood vessels and heart.
2. Type 2 diabetes, non-insulin-dependent, once called “senile” diabetes, characterised by blood glucose levels that are not excessively high but in which insulin production is defective, although not lacking. This type of diabetes is found mainly in people who are overweight or elderly.

Why it is done
This test mainly shows the risk of developing diabetes, a disease linked to a rise in blood glucose, i.e. the glucose circulating in the blood. The concentration of glucose in the blood must be constant at all times, as it is the result of a balance between the natural removal of glucose from the blood, which cells use for energy (glycolysis and glycogen synthesis), and the entry of glucose into the blood from food and the body’s stores (gluconeogenesis and glycogenolysis). It is a screening test, i.e. a first pointer for the doctor: if blood glucose values are high and diabetes is therefore suspected, the test must be repeated, and if the result is high again the laboratory can now diagnose diabetes. A further test is sometimes recommended, because doubts may remain in some cases (for example, when the second blood test shows a glucose value that is not high but is still too close to the upper limit). To reach a definite diagnosis, the further test usually recommended is the “oral glucose tolerance test”, which monitors blood glucose after taking 75 grams of glucose and again after two hours, to see what happens in the body after this glucose load and whether glucose levels are too high after two hours. However, if blood glucose is already high in the morning, it is important not to take the glucose and not to continue with the test, as this could cause complications. If the values are high after this further test, a diagnosis of “established diabetes” is made. To keep diabetes under control over time and check that the treatment prescribed by the doctor is right, a “fasting and post-meal glucose test” must then be done at regular intervals, i.e. blood tests taken both in the morning on an empty stomach and two hours after lunch, to show how the body is responding to the medicines or diet prescribed and check that blood glucose does not rise too much after lunch. “Diabetes in pregnancy” is a special case. Pregnancy stimulates glucose production in the body, which can cause complications in the baby, so an initial screening test is recommended for every pregnant woman to rule out diabetes. This test is called the “mini glucose challenge test”: the pregnant woman has a blood test in the morning on an empty stomach, after taking 50 grams of glucose and again after three hours.

How it is done
It is a simple blood test that must be done after fasting for at least 12 hours, because glucose is strongly affected by the food eaten during the day. Medicines do not affect the result, but it is always advisable to tell your doctor so that they can assess the report as a whole.