What is a Glucose Blood Test?

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  • Written By: wiseGEEK Writer
  • Edited By: O. Wallace
  • Last Modified Date: 01 January 2019
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The glucose blood test can be one of several types of blood tests that evaluate the amount of glucose, or what is sometimes called “sugar” in the blood. Any number of reasons might exist for people to have a test. It could be part of routine diagnostics, to look for abnormal glucose levels, high or low, or to rule in or out certain risk factors or conditions.

There are many glucose blood test variations. The first simply takes a small sample of blood, via needle, at any time of day and evaluates it to get glucose levels. A second type is not that different except that people may need to fast for at least eight hours prior to getting the test. If more information is needed, doctors sometimes have people eat an hour or two before a test, to see how blood glucose levels change.

Other tests that could be performed include the one-hour challenge test, where people drink a certain amount of a glucose drink to see how the sugar clears their bodies. Pregnant women take a form of this too, usually in the end of the second trimester, as part of screening for gestational diabetes. There are several variations of these challenge tests, but the most unpleasant part, according to many, is drinking the glucose drink. Refrigeration tends to help cut taste, which is very sweet.


When problems with glucose levels are suspected and because changes in levels that exceed the norm can indicate serious disease, it’s possible for people to undergo several different types of tests. This would mean patients would have to follow either the doctor’s or lab’s instructions on exactly what to do in each case, so that the most accurate readings are obtained. For instance, those instructed to take a fasting glucose blood test should not forget about having eaten something for breakfast and head to the lab. If a mistake is made in the preparation for a test, people should alert the lab and possibly make arrangements for testing the next day.

The results from a single glucose blood test can upset people. They might see a high sugar reading and assume they have diabetes or some other condition. Especially with conditions like diabetes, retesting is usually recommended to verify results. When people feel even a second test cannot be right, they could ask for a third. Generally, when several tests show a consistent finding, though, certain conditions are likely and could need treatment right away.

The last type of glucose blood test is not performed in a lab or a hospital. Some people have glucose monitors at home and take small samples, often much smaller than lab test samples, of their blood each day to monitor blood sugar levels. These may be recommended to people with certain forms of diabetes, especially to those who must have frequent blood sugar readings to determine types of treatment needed.



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