Diabetes, high blood glucose, was affecting more than 23 million Americans in 2007, or nearly 8 percent of the population, the American Diabetes Association reports. Diabetes, diagnosed by abnormal elevations in blood glucose, or high blood sugar, occurs when the pancreas doesn't make enough insulin or when cells can't utilize insulin properly. Insulin helps cells to take up glucose for energy. As a result of impaired insulin use, glucose accumulates in the blood rather than being used by the cells. A number of tests can diagnose diabetes from glucose levels.
Types
Blood tests give the most accurate readings for diagnosing diabetes. At one time urine tests were also used, but they don't give exact readings and vary depending on the last meal eaten.
Timing
Proper timing of blood tests is essential for diagnosing diabetes, because blood glucose varies according to the timing of the last meal. Fasting blood sugars measure blood glucose after abstaining from food or drink for 10 hours, while random blood sugars measure blood glucose any time during the day. Oral glucose tolerance tests in the doctor's office measure blood glucose after a large amount of glucose is consumed. Blood samples are taken 30 minutes, one hour, two hours and three hours after a person drinks 75 grams of glucose, or 100 grams for pregnant women undergoing the test, endocrinologist James Norman, M.D. of the Norman Parathyroid Clinic, explains. Glycated hemoglobin A1C, which measures the amount of glucose attached to hemoglobin, gives an average of blood glucose readings over two to three months.
Results
Fasting blood glucose normally ranges from 70 to 99 mg/dL, or milligrams per deciliter. Random blood glucose at any time should measure below 200 mg/dL. A1C levels should fall below 6.5 percent, MayoClinic.com reports. A two hour glucose level of less than 140 mg/dL in the oral glucose tolerance test is considered normal, the National Institute of Diabetes and Digestive and Kidney Disorders, the NIDDK, states.
Diagnosis
A single reading cannot diagnose diabetes, and slightly elevated glucose levels also don't diagnose diabetes. Fasting blood glucose levels of 126 mg/dL or higher on two separate occasions are diagnostic of diabetes, while A1C levels over 6.5 on two separate occasions are also required to diagnose diabetes. Two hour glucose levels between 140 to 199 mg/dL indicate impaired glucose tolerance, while levels over 200 indicate diabetes, the NIDDK states. People who have an elevated glucose level that's not high enough to be considered diabetes have pre-diabetes and are at risk for developing diabetes.
Interfering Factors
Certain diseases and medications can temporarily raise blood glucose levels. Severe illness or stress and corticosteroid medications and certain diuretics can temporarily raise blood glucose levels above normal, Dr. Norman states.
