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Type 2 Diabetes: Is It More Than Just Blood Sugar?
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Diagnosis
Type II diabetes is diagnosed with the following blood tests:
- Fasting blood glucose test (FGT): positive diagnosis of diabetes or pre-diabetes requires values higher than 126 mg/dL after eight hours of fasting on two separate occasions.
- Random (non-fasting) blood glucose: values higher than 200 mg/dL, accompanied by increased thirst, urination, and fatigue, cause suspicion of diabetes that must be confirmed with a fasting blood glucose test.
- Oral glucose tolerance test (OGTT): positive diagnosis of diabetes or pre-diabetes requires values higher than 200 mg/dL two hours after consuming a glucose solution.
A positive diagnosis of diabetes requires positive results on any one of the three listed tests, with confirmation from a second positive test on a different day. The fasting plasma glucose test is preferred for diagnosing type I and type II diabetes, and pre-diabetes. This convenient test is most reliably performed in the morning after eight hours of fasting, on two separate occasions. FGT values from 70–99 mg/dL are considered normal. Fasting glucose levels of 100–125 mg/dL may indicate a form of pre-diabetes called impaired fasting glucose (IFG). Individuals with IFG have an increased probability of developing type II diabetes in the future. A fasting glucose level 126 mg/dL, in conjunction with a positive OGTT on a separate testing occasion, indicates diabetes.
The random (non-fasting) glucose test can be performed at any time of day, regardless of previous food intake. Diabetes is suspected when blood glucose levels above 200 mg/dL are present in combination with classic diabetic symptoms such as increased thirst and urination, and fatigue. Diagnosis of diabetes requires a positive fasting blood glucose test or oral glucose tolerance test to be performed on a different occasion.
The oral glucose tolerance test can be used to diagnose diabetes or pre-diabetes. The patient is required to fast for eight hours and then drink a solution containing 2.6 oz (75 g) of glucose dissolved in water. Blood glucose levels are then measured at separate points over a three-hour time interval. A value less than 140 mg/dL is considered normal. Values from 140–200 mg/dL may indicate pre-diabetes. A value over 200 mg/dL, in conjunction with a positive FGT on a separate testing occasion, indicates diabetes.
Gestational diabetes is diagnosed with the OGTT. Glucose levels are normally lower during pregnancy, so the threshold values for diagnosis are proportionally lower. The presence of two plasma glucose values meeting or exceeding any of the following levels results in a diagnosis of gestational diabetes: a fasting plasma glucose level of 95 mg/dL, a one-hour level of 180 mg/dL, a two-hour level of 155 mg/dL, or a three-hour level of 140 mg/dL. Some practices deem a 1.7 oz (50 g) glucose solution with one-hour testing to be acceptable.
The hemoglobin A1c (HbA1c) test is used primarily to monitor the quality of glucose control over several weeks. Controlled blood glucose helps to minimize the development of complications caused by chronically elevated glucose levels, such as progressive damage to body organs. The HbA1c test is an overall picture of the average amount of glucose in the blood over the previous few months. HbA1c is the term for glycosylated (glucose-carrying)
hemoglobin in red blood cells. It is a measurement of how successful the employed treatments are at controlling blood sugar values. The HbA1c test can determine how severe blood sugar fluctuations have been in newly diagnosed diabetics and indicate the need for treatment adjustments in the medication or diets of known diabetics. Physicians may perform HbA1c tests on a patient several times a year to verify that good control is being maintained. The HbA1c test will not reflect temporary, acute fluctuations in blood glucose. A 1% change in HbA1c reflects a fluctuation of approximately 30 mg/dL in average blood glucose. An HbA1c value of 6% corresponds to an average blood glucose value of 135 mg/dL, while an HbA1c of 9% corresponds to an average blood glucose value of 240 mg/dL. The closer the HbA1c can be kept to 5% or 6%, the better diabetic control. Risk of diabetic complications increases with increased values of HbA1c.
A urinalysis followed by a blood test for ketones and pH is used in diagnosing ketoacidosis. Type I diabetes may also require a test for insulin level to determine whether it is very low or absent. A test for C-peptide levels, a byproduct of insulin production, is also often performed.
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Author Info: Maria Basile PhD, Thomson Gale, Gale, Detroit, Gale Encyclopedia of Genetic Disorders Part II, 2005 |
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