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glucose tolerance test
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What is a glucose tolerance test?
The glucose tolerance test assesses the body's ability to metabolize glucose, the primary sugar in the blood. It is typically performed on individuals with normal or slightly elevated blood-sugar to measure the body's tolerance to sugar under induced stress.
During the procedure, blood and urine samples are taken to determine glucose levels at different intervals. For example, in a common procedure, a person who has been fasting will have an initial blood sample taken, then ingest 50β100 grams of glucose dissolved in water. Further blood and urine samples are taken 30 minutes, 1 hour, 2 hours, and 3 hours later.
The oral glucose tolerance test can confirm or rule out diabetes mellitus when a fasting blood glucose test is not definitive. It is also used during pregnancy to detect early glucose intolerance, known as gestational diabetes mellitus, which could pose a risk to the infant.
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Why do doctors use a glucose tolerance test?
Doctors use a glucose tolerance test to assess how well your body metabolizes glucose, the main sugar in your blood. It helps diagnose conditions like diabetes mellitus and gestational diabetes mellitus, especially when other tests are inconclusive. During the test, blood samples are taken over a few hours after you consume a specific amount of glucose. The results help doctors see how your blood sugar levels change and whether they return to normal within a certain time frame.
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How is a glucose tolerance test performed?
The glucose tolerance test assesses the body's ability to metabolize glucose, the primary sugar in the blood. After taking an initial blood sample from a fasting individual, they will empty their bladder and then ingest 50β100 grams of glucose dissolved in water. Blood and urine samples are taken 30 minutes, 1 hour, 2 hours, and 3 hours later for glucose determination.
Normally, glucose concentration in the blood rises to about 140 mg/100 ml within 45β60 minutes and returns to 80β120 mg/100 ml within 1.5β2.5 hours. The most valuable diagnostic point is at 2 hours, when the value should be less than 120 mg/100 ml. A glucose tolerance test is used to confirm or exclude a diagnosis of diabetes mellitus when a fasting blood glucose test result is not definitive.
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What happens to your blood sugar during the test?
During a glucose tolerance test, blood sugar levels are monitored to assess how well your body metabolizes glucose.
Typically, after a fasting blood sample is taken, you'll consume a specific amount of glucose. Blood samples are then taken over a few hours. In individuals without impaired sugar metabolism, blood glucose rises, peaking within 45β60 minutes, and returns to normal levels within 1.5β2.5 hours. The most valuable diagnostic point is at 2 hours, when the value should be less than 120 mg/100 ml.
In people with diabetes, blood sugar levels rise higher and take longer to return to normal. During pregnancy, a prolonged elevation of blood sugar may indicate slower carbohydrate use or glucose absorption.
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What can the results of a glucose tolerance test show?
A glucose tolerance test assesses how well your body metabolizes glucose after ingesting a specific amount. It can reveal vital information about your body's sugar metabolism, especially in those with normal or slightly elevated blood sugar.
In individuals with impaired sugar metabolism, such as those with diabetes mellitus, the test results will show a blood-sugar-level curve that rises higher than normal and returns to normal more slowly. This curve can also be seen in nondiabetic persons during acute illness, after trauma, when on a low-carbohydrate diet, in elderly persons with hardening of the arteries or heart disease, and in middle-aged persons who are markedly overweight.
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How does a glucose tolerance test help diagnose diabetes or other health problems?
The glucose tolerance test assesses how well your body metabolizes glucose, the main sugar in your blood. It helps diagnose diabetes and other conditions affecting sugar metabolism.
During the test, you'll fast, then drink a glucose solution. Blood and urine samples are taken over a few hours to monitor glucose levels. In individuals without diabetes, blood glucose rises and then returns to normal within 2-3 hours. Those with diabetes show a higher and slower return to normal on the blood-sugar-level curve.
The oral glucose tolerance test can confirm diabetes when fasting blood glucose results are unclear. It's also used during pregnancy to detect gestational diabetes, which could harm the infant if untreated.
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glucose tolerance test, procedure to assess the ability of the body to metabolize glucose, the principal type of sugar found in the blood.
In persons with normal or slightly elevated blood-sugar levels, the body tolerance to sugar is measured in a stressful situation induced by administering a large amount of glucose. The most common procedure is to take an initial blood sample from a fasting individual, have the individual empty his or her bladder, and then administer orally 50β100 grams of glucose (usually 1 gram of glucose per kilogram of ideal body weight) dissolved in water. Samples of blood and urine for glucose determination are obtained 30 minutes, 1 hour, 2 hours, and 3 hours later. Normally the concentration of glucose in the blood will rise to about 140 mg/100 ml within 45β60 minutes and will return in 1 1/2β2 1/2 hours to the normal range of 80β120 mg/100 ml. The most valuable diagnostic point is 2 hours, when the value should be less than 120 mg/100 ml.
A fasting glucose tolerance test can convey important information about decreased tolerance to sugar in persons suffering from an impairment of sugar metabolism, such as diabetes mellitus. In these individuals a decreased tolerance to sugar is manifested by a blood-sugar-level curve that rises higher than, and returns more slowly to, normal. This type of curve may also be seen in nondiabetic persons during acute illness, after trauma, or when on a low-carbohydrate diet; it may also be observed in elderly persons with hardening of the arteries or heart disease and in middle-aged persons who are markedly overweight.
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An oral glucose tolerance test is used to confirm or exclude the diagnosis of diabetes mellitus when a fasting blood glucose test result is not definitive (i.e., greater than the upper range of the normal value but less than the diagnostic level for diabetes). Even if a blood glucose test is obtained after fasting 10β12 hours and the level is above 140 mg/100 ml, it is important to confirm the result with a second determination to rule out other factors that may have given a one-time abnormal test result.
The oral glucose tolerance test measures the response of the body to a challenge load (an amount calculated to evoke a response) of glucose. It most often is used during pregnancy to detect early glucose intolerance that could pose a significant risk to the infant if the condition progressed to gestational diabetes mellitus. After a fasting blood glucose test result has been obtained, 75 grams of glucose (100 g if the patient is pregnant) is administered and blood samples are taken every 30 minutes for 2 hours. In patients with diabetes, the blood glucose value will rise to a higher level and remain higher longer than in individuals who do not have diabetes.
A simpler but less-reliable screening test is the 2-hour postprandial blood glucose test. This test is performed 2 hours after intake of a standard glucose solution or a meal containing 100 grams of carbohydrates. A plasma glucose level above 140 mg/100 ml indicates the need for a glucose tolerance test.