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Tests and Diagnosis for Type 2 Diabetes

By Laurie Marbas, M.D. ; Updated August 14, 2017

The typical test for Type 2 Diabetes is a blood glucose test. Normal concentrations of glucose in the blood are between 60 mg/dL and 100 mg/dL. This can be tested by fasting for eight to 12 hours (drinking only water) prior to taking a blood test. A normal two-hour glucose tolerance test is less than 140 mg of glucose per one dL of blood. Mildly abnormal results indicate impaired fasting glucose that often precedes an eventual diabetes diagnosis.

Another test commonly performed is a hemoglobin A1c test. A normal level of hemoglobin A1c is less than 5.7 percent, or between 4 and 5.6 percent. Hemoglobin is found in red blood cells and contains iron that transports oxygen to tissues. There is a component of the hemoglobin called A1c. The A1c is formed by the chemical interaction of glucose and hemoglobin, which occurs throughout the life span of a red blood cell (about 120 days). The rate at which A1c is formed is directly proportional to the blood glucose concentration. The higher the glucose level the more A1c is formed. Therefore hemoglobin A1c is a great marker for the average blood glucose levels in the previous three months and is often used to monitor how well Type 2 diabetes is being controlled in an individual. Levels of hemoglobin A1c (HbA1c) can be assessed by taking a glycohemoglobin test.

Other Diseases That Should Be Ruled Out

Some other diseases that cause elevated blood glucose levels should be ruled out if there are any symptoms. These associated conditions include:

1) Cushing disease is a condition of excess cortisol production that starts with a pituitary tumor in the brain called an adenoma. Cushing disease is affiliated with increased glucose concentrations in the blood and insulin resistance.

2) Acromegaly is caused by a benign pituitary tumor called an adenoma that causes an overproduction of growth hormone.

3) Pheochromocytoma is caused by a benign adrenal tumor that results in an excess of epinephrine and norepinephrine being released into the bloodstream, resulting in a rise in blood pressure.

4) Hyperthyroidism is an overactive thyroid gland that releases too much thyroid hormone.

Diagnosis of Type 2 Diabetes

Diabetes can be diagnosed by any of the following methods, assessed on two different occasions:

1) A fasting (not eating for eight to 12 hours) plasma glucose concentration greater than 126 mg/dL. Glucose intolerance, or pre-diabetes, is a concern with blood glucose concentrations between 100 mg/dL and 125 mg/dL.

2) A two-hour oral glucose tolerance test result of 200 mg/dL or greater on two different occasions.

3) A random plasma glucose of 200 mg/dL or greater when diabetes symptoms are present, such as increased thirst and urination, unexplained weight loss, blurry vision and/or increased urination at night.

4) Hemoglobin A1c greater than or equal to 6.5 percent. Pre-diabetes is a concern with A1c levels between 5.7 and 6.4 percent.

5) There is still some debate about using hemoglobin A1c for diagnosis of Type 2 diabetes because it can be affected in a variety of conditions, such as sickle cell disease, thalassemia, anemia, kidney and liver disease and ingestion of vitamin C and E supplements. However, tracking the concentration of hemoglobin A1c is crucial in the management of Type 2 diabetes.

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