Diabetes Test For Diagnosis
Medical Testing Procedures to Diagnose Diabetes

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Tests For Diabetes

A diagnosis of diabetes mellitus is based upon the level of blood glucose in a blood sample.

Blood Glucose Levels Rise and Fall

The amount of glucose in the blood varies according to when and what you eat. Typically, blood glucose is highest immediately after eating, and lowest after fasting for 8-10 hours. After eating a large meal, a person's blood sugar will rise up to about 140 milligrams of glucose per deciliter of blood (mg/dL). After fasting all night, most people have a blood sugar level somewhere between 70 and 110 milligrams of glucose per deciliter. Untreated diabetics have higher blood sugars after fasting and after eating.

Testing For Diabetes

To check for diabetes, your physician tests your blood sugar level in a sample of your blood. The test result shows if you have diabetes and if so, what type. But doctors do not diagnose diabetes on the basis of a single test. Typically they conduct two or more glucose tests before confirming their diagnosis. The most common tests to measure glucose are the fasting plasma glucose test, the random blood sugar test, and the oral glucose tolerance test.

Fasting Plasma Glucose Test (FPG)

The fasting plasma glucose test is the preferred test for diagnosing type 1 or type 2 diabetes and is usually performed in the morning. Before taking this test, you cannot eat anything for 8 to 10 hours. Blood will be drawn from a vein in your arm and sent to a laboratory for testing. If your fasting glucose level is 100 to 125 mg/dL, you have a form of pre-diabetes called impaired fasting glucose (IFG), meaning that you are more likely to develop type 2 diabetes but do not have it yet. A level of 126 mg/dL or above, confirmed by repeating the test on another day, means that you have diabetes.

Random Blood Glucose Test

Many instances of diabetes are found during routine physical examinations when blood is drawn for other tests. Since you probably won't have fasted before these physical exams, your blood sugar may be high. But it shouldn't be higher than about 200 mg/dL. If your random blood glucose is higher than 200 mg/dL - especially if you have other symptoms of diabetes such as increased urination, increased thirst, or unexplained weight loss - your doctor will probably suspect diabetes and will suggest a fasting plasma glucose test.

Oral Glucose Tolerance Test (OGTT)

In this test, a person consumes a drink containing glucose dissolved in water. Blood is then drawn in timed intervals over a three-hour period. If your blood glucose level is between 140 and 199 mg/dL 2 hours after drinking the liquid, you have a form of pre-diabetes called impaired glucose tolerance or IGT, meaning that you are more likely to develop type 2 diabetes but do not have it yet. A 2-hour glucose level of 200 mg/dL or above, confirmed by repeating the test on another day, means that you have diabetes.
This test is often used to check pregnant women for gestational diabetes. It is rarely used to diagnose diabetes in other patients, because it is cumbersome and time-consuming.

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Carbs-Information.com provides general information about the glycemic index (GI), glycemic load (GL), low GI diets, GI values for all food groups, health problems of high blood glucose including metabolic disorders such as pre-diabetes, impaired glucose tolerance, insulin resistance, hyperinsulinism as well as type 1 and type 2 diabetes. But no information is intended as a substitute for medical advice. Copyright 2003-2021.