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Diabetes Diagnosis

What Is Diabetes?

Diabetes is a medical condition that affects your body’s ability to produce insulin, use insulin effectively, or both. Insulin is a hormone that allows your body to use glucose, or sugar, for energy. It acts as a "bridge" that allows the sugar to go from the blood and into the cell.  If the sugar stays in the blood, the unused glucose will build up in your body, which can lead to nerve and organ damage.

A physician can also diagnose you with prediabetes. This condition indicates a high risk of developing diabetes. Making healthy lifestyle changes may help prevent progressing from prediabetes to type 2 diabetes.

Because diabetes can be a dangerous and life-threatening condition, it is important that it is diagnosed as early as possible. The early stages of diabetes may not cause any symptoms. Recognizing high blood glucose levels as quickly as possible can reduce the complications associated with diabetes.

What Tests Are Used to Diagnose Diabetes?

Four major tests can diagnose diabetes. Because there are three main diabetes types–type I, type II and gestational diabetes–a physician will recommend the appropriate test for you. All tests require a blood sample.

The A1C test measures how much glycated hemoglobin, a protein found in the red blood cells. When blood sugar levels are high, more sugar attaches to the hemoglobin. Since hemoglobin turns over every two to three months this test measures how your blood sugar levels have averaged over two to three months. This can indicate to your physician that your blood sugar has been higher than normal over this period of time. Your doctor may choose to confirm these results on another day.  You do not have to fast for this test.

The fasting plasma glucose (FPG) test is performed when you have not had anything to eat or drink except water for eight hours. A high fasting glucose level on two separate occasions can be used to diagnose prediabetes and diabetes.

The oral glucose tolerance test (OGTT) is a diagnostic diabetes test most commonly used to diagnose gestational diabetes. It can also diagnose type 2 diabetes. To test for type 2 diabetes, the test is performed over two hours. A physician will first take a sample of blood when you are fasting, and then have you drink a sweet beverage that contains 75 grams of glucose. Two hours later, they will test your blood again to see if your body effectively processed the glucose.

The fourth test type is the random plasma glucose test. This test checks your blood sugar levels randomly at any time of day, without fasting. Two high random glucose levels are needed to diagnose diabetes unless you have signs and symptoms of diabetes.

Who Should Be Tested for Diabetes?

If you are older than age 45, the American Diabetes Association recommends testing for diabetes. However, if you have diabetes risk factors or symptoms, you may need earlier testing. Indications for testing people younger than 45 include being overweight (body mass index of 25 or more) plus one or more of the following:

  • a family history of diabetes
  • a history of gestational diabetes
  • giving birth to a baby weighing more than 9 pounds
  • having been diagnosed with polycystic ovary syndrome
  • being sedentary
  • having conditions that increase your risk for insulin resistance
  • previous diagnosis of prediabetes or high blood sugar
  • HDL cholesterol levels less than 35 mg/dl
  • triglyceride levels higher than 250 mg/dl
  • diagnosis of high blood pressure
  • taking medications for high blood pressure
  • being a member of a high-risk genetic population, such as African-American, Asian-American, Hispanic, Native American, or Pacific Islander

Examples of diabetes symptoms include unexplained fatigue, increased urination, constant thirst or hunger, blurry vision, and sores that will not heal.

This information is a summary. Always seek medical attention if you are concerned you may be experiencing a medical emergency.

Risks of Diabetes Diagnosis Tests

Blood samples for testing presents minimal physical risk. However, these tests can sometimes yield a false positive or negative result. For example, if you are anemic, your A1C results may be inaccurate because anemia affects the amount of hemoglobin in the blood.

Results of Diabetes Diagnosis Tests

Unless you have diabetes symptoms, diabetes diagnosis usually requires two consecutive tests. The following are general diagnostic values for diabetes:

For the A1C test:

For the FPG test:

  • less than 100 mg/dl is considered normal
  • 100 to 125 mg/dl is considered prediabetes
  • 126 mg/dl or higher is considered diabetes

For the oral glucose tolerance test (OGTT) (type 2 diabetes only):

  • less than 140 mg/dl is considered normal
  • 140 to 199 mg/dl is considered prediabetes
  • 200 mg/dl and higher is considered diabetes

For the random plasma glucose test:

  • 200 mg/dl or greater could indicate diabetes

Treatment for Positive Diabetes Testing

Your physician can use your results and symptoms to recommend a diabetes treatment plan. Some patients can control diabetes through a healthy diet and exercise plan, with weight loss as needed. Others may require medications along with diet and exercise to help manage blood sugar levels.

Making healthy choices to either reduce your risk of developing diabetes or to control your diabetes is vital for your overall health. Good blood sugar control can prevent diabetes complications such as kidney or eye disease, or nerve damage.

Content licensed from:

Written by: Written by Rachel Nall, BSN
Medically reviewed on: May 01, 2014: Peggy Pletcher, MS, RD, LD, CDE

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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