The glucose tolerance test is a timed test of the glucose concentration in both the blood and urine.
This test is used to confirm or rule out diabetes and is a
definitive test for diagnosing hypoglycemia. After fasting overnight, the client is given a concentrated amount of glucose dissolved in a flavored, water-based drink. Blood and urine samples are collected over a three- to four-hour period.
In health, the insulin response is immediate and in sufficient quantity to tolerate the glucose load and to move the glucose from the blood to the cells of the body. There will be a minimal and temporary rise in plasma glucose levels within the first hour, with a return to normal levels in the second hour of testing .
definitive test for diagnosing hypoglycemia. After fasting overnight, the client is given a concentrated amount of glucose dissolved in a flavored, water-based drink. Blood and urine samples are collected over a three- to four-hour period.
In health, the insulin response is immediate and in sufficient quantity to tolerate the glucose load and to move the glucose from the blood to the cells of the body. There will be a minimal and temporary rise in plasma glucose levels within the first hour, with a return to normal levels in the second hour of testing .
Normal Range
Fasting
70-115 mg/dl
30 min
less than 200 mg/dl
1 hour
less than 200 mg/dl
2 hours
less than 140 mg/dl
3 hours
70-115 mg/dl
4 hours
70-115 mg/dl
70-115 mg/dl
30 min
less than 200 mg/dl
1 hour
less than 200 mg/dl
2 hours
less than 140 mg/dl
3 hours
70-115 mg/dl
4 hours
70-115 mg/dl
Variations from Normal. Individuals who are diabetic or hypoglycemic will not be able to tolerate the glucose load administered during the glucose tolerance test. Diabetic clients will exhibit increased glucose levels that exceed 190 mg/dl at one hour; 165 mg/dl at two hours; or 145 mg/dl at three hours. Different types of diabetes can be identified by the glucose elevation at specific time intervals.
Type II or noninsulin-dependent diabetes mellitus (NIDDM), which is
characterized by a delay in the secretion of insulin or a decreased number of insulin receptor sites, displays an elevated glucose level until the two-hour point. Type I or insulin-dependent diabetes mellitus (IDDM), which may be characterized by a lack of insulin or the absence of its secretion, displays an elevated glucose level throughout the test period. Gestational diabetes also displays an elevated glucose level throughout the test period.
The hypoglycemic individual will also have trouble handling the glucose load administered during the glucose tolerance test. The glucose load will trigger high insulin levels, which will in turn mobilize the glucose to leave the blood. Consequently the blood glucose level will drop below normal at two hours, and remain low for the remainder of the test period.
Interfering Circumstances. Circumstances surrounding the patient's lifestyle can interfere with test results. Smoking and exercise during the test period can stimulate glucose levels. Prolonged inactivity and weight reduction dieting prior to testing can produce inaccurate results.
Specific drugs and medications will interfere with glucose tolerance.
These include insulin, large doses of aspirin, oral contraceptives, estrogens, anti-inflammatory drugs, nicotine, lithium, and thiazide diuretics.
