Glucose tolerance test: how it is done and normal values

What is the glucose tolerance test?

Also known medically with the name of glucose tolerance curve, it is a type or blood test specially used in the diagnosis of prediabetes, diabetes mellitus type 2 (the most common), or gestational diabetes during pregnancy. Why? Fundamentally because helps to know how the body is able to break down sugar (glucose).

It should not be confused with sugar test in pregnancy, which is habitual and medically known by the name of O'Sullivan test, and that is carried out between weeks 24 and 28 of gestation, although depending on the Autonomous Community in which the pregnant woman is (in Spain) it is possible to have two measurements, one in the first trimester or the other. next a little later.

This time we will talk about one of the most common glucose tolerance tests, called oral glucose tolerance test (PTGO). There is also the one known as intravenous glucose tolerance test (PTGIV), but it is less common and is rarely used for the diagnosis of diabetes.

How the glucose tolerance test is performed: the steps you must follow

Days before the completion of the tolerance test, it is advisable to follow a normal, routine lifestyle, eating normally. Then, it is essential not to eat or drink anything during the 8 hours prior to the time of the test. Similarly, you can not eat or drink anything during the test.

A sample of blood is taken before taking the glucose solution, which will allow knowing the fasting blood glucose values, before having ingested anything.

Then you must drink a glucose solution (It can be glucose or dextrose), which at the beginning can be somewhat unpleasant because it tends to taste very, very sweet. Many doctors tell the patient that its taste is similar to a soda, but the truth is that it is actually much sweeter. The most common is that the amount of glucose reaches 75 grams.

Later, New blood samples will be taken every 30 to 60 minutes immediately after ingesting the glucose solution. It is possible that a third blood sample may be taken.

Since it is a test that can take up to 3 hours, it is essential that the person remain in the laboratory. It is not advisable to go for a walk or exercise. Neither obviously eat anything or drink anything except the glucose solution administered by the laboratory.

That is, we can summarize the glucose tolerance test as follows:

  1. A first fasting blood sample is obtained.
  2. The glucose solution is swallowed, slowly and little by little.
  3. 30 or 60 minutes are expected and a second blood sample is obtained.
  4. Another 60 minutes are expected (2 hours in total), and a third and final blood sample is obtained.

Values ​​of the glucose tolerance test

The reference values ​​of the glucose tolerance curve refer to the value of glucose 2 hours after the ingestion of glucose. And are next:

  • Normal fasting values: 60 to 100 mg / dl.
  • Normal:lower than 140 mg / dl.
  • Prediabetes:between 140 to 199 mg / dl.
  • Diabetes:equal to or greater than 200 mg / dl.

Thus, if the patient has fasting glucose values ​​above 126 mg / dl, and a blood glucose equal to or greater than 200 mg / dl 120 minutes (2 hours) after having ingested the glucose solution, it is quite likely that you suffer from diabetes.

Values ​​of the oral glucose tolerance test (PTGO)

It is also possible to take into account other values ​​considered equally normal depending on the time elapsed after ingestion of the glucose solution. Usually, for a glucose tolerance test with 75 grams of glucose, the normal values ​​are as follows:

  • Fasting:60 to 100 mg / dl.
  • 1 hour later:less than 200 mg / dl.
  • 2 hours later:less than 140 mg / dl.

This test is usually performed in patients with a high fasting blood glucose level (above 125 mg / dl), but is not so high as to be able to be diagnosed with diabetes. This article is published for informational purposes only. It can not and should not replace the consultation with a Physician. We advise you to consult your Trusted Doctor. ThemesBlood test

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