Tests for Diabetes

American Diabetes Association Complete Guide to Diabetes
by American Diabetes Association

(Page 2 of 2)

Although your physician may suspect that you have diabetes because of your symptoms, the only sure way to tell is with blood tests. Blood tests are used to diagnose both type 1 and type 2 diabetes, as well as gestational diabetes. Your doctor may repeat your blood tests to be sure of the diagnosis.

The blood tests are based on the fact that diabetes keeps your blood glucose, or sugar, levels above normal some or all of the time. Your blood glucose levels may be high even though you haven't eaten recently. In addition, your body cannot get rid of the extra glucose that appears in the blood after eating.

Random plasma glucose tests are the simplest way to detect diabetes. This test measures the amount of glucose in the blood at any given time and is done without fasting. If you have obvious symptoms of diabetes and the amount of glucose in your blood is 200 mg/dl or higher, your doctor will diagnose diabetes. Symptoms of diabetes include frequent urination, intense thirst, blurred vision, unexplained weight loss, and extreme tiredness.

The preferred method for diagnosing diabetes is the fasting plasma glucose test. For this test, your doctor will ask you not to eat for at least 8 to 10 hours. Then, a sample of your blood is taken, and the amount of glucose present in the blood is measured. Normally after fasting, the amount of glucose is less than 110 mg/dl. But when the amount of blood glucose is greater than 126 mg/dl, the doctor will suspect diabetes. In diabetes, extra glucose remains in the blood, even after fasting, because it cannot enter the body's cells. This is due to a lack of insulin or resistance to the action of insulin. Doctors usually make a firm diagnosis of diabetes when two fasting plasma glucose tests, done on different days, are over 126 mg/dl.

If your test results are greater than 110 mg/dl but less than 126 mg/dl, you may be diagnosed with impaired fasting glucose. This is not diabetes, but sometimes occurs before diabetes, usually type 2 diabetes, develops. Some people with impaired glucose tolerance never get diabetes. However, some of the same problems that result from having diabetes also occur in people with impaired glucose tolerance. If you have been diagnosed with impaired glucose tolerance, your physician will want to watch carefully for diabetes. Also, you need to talk with your doctor about reducing your risk of heart disease, keeping your weight in the healthy range, and exercising regularly to lower your chances of developing diabetes.

Certain pregnant women with no history of diabetes are at high risk for developing gestational diabetes. These are women who are 25 years of age or older, are overweight, have a parent or sibling with diabetes, or are Hispanic, Native American, Asian, or African-American.

If you have any of these characteristics, your obstetrician will screen you for gestational diabetes with a glucose challenge. This is done between the 24th and 28th weeks of pregnancy. At this time, the hormones of pregnancy naturally begin to cause temporary insulin resistance that lasts until the baby is born. The glucose challenge helps your doctor determine whether your body is able to overcome the insulin resistance on its own. You are given a glucose drink to finish at a certain time, without regard to eating. If the glucose in your blood 1 hour later is 140 mg/dl or above, you may have gestational diabetes. Your doctor will need to give you another test, for which you may need to fast, for a firm diagnosis.

Type 1 or Type 2?

If tests reveal that you have diabetes (and you're not pregnant), your doctor must then decide whether you have type 1 or type 2 diabetes. Although the symptoms and blood test results are similar for both type 1 and type 2 diabetes, the causes are very different.

It will help your doctor to know whether there has been type 1 or type 2 diabetes in your family. Your age is not the only clue about what type of diabetes you have. It's true that most people younger than age 20 who show signs of diabetes have type 1 diabetes and that most people diagnosed with diabetes when they're over age 30 have type 2 diabetes. But there are exceptions. In some cases, families carry a genetic trait for developing type 2 diabetes as young people. And in some Native American families, obesity is so prevalent that children as young as 10 years old have type 2 diabetes.

If you are overweight or obese, it is more likely that you have type 2 diabetes.

If you suddenly developed signs of diabetes, such as frequent urination, unusual thirst and hunger, and weight loss, perhaps after an illness, and are a young adult or child, it is more likely that you have type 1 diabetes.

If you are not overweight and there are ketones in your urine, it is more likely that you have type 1 diabetes (see Chapter 5 on ketone testing).

If you are African American or Hispanic American, are older than 50, are overweight, and haven't been feeling quite "right" for a long time, it is more likely that you have type 2 diabetes.

If your doctor treats you with insulin injections, you could have either type 1 or type 2 diabetes.

Diabetes: Fact or Myth?

"I used to have type 2 diabetes, but now I have type 1 diabetes. My doctor put me on insulin last year."

Lots of people, over 40 percent of adults with diabetes, use insulin. But because there are about 90 adults with type 2 diabetes to every 5 adults with type 1 diabetes, this means there are a lot of people with type 2 diabetes taking insulin. People with type 1 diabetes must use insulin to make up for their pancreas no longer making it. You don't necessarily have type 1 diabetes just because you have to take insulin. Many people with type 2 diabetes need extra insulin to overcome their body's resistance to the insulin already being made by the pancreas.

Type 1 diabetes and type 2 diabetes, while having a lot in common, are two different diseases. They have different causes. The type of diabetes you have does not change as you age or if you lose or gain weight or change treatment.

Copyright © 2000 by American Diabetes Association. Excerpted by permission of Bantam, a division of Random House, Inc. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.

About the Author

The American Diabetes Assocation is the nation's leading voluntary health organization supporting diabetes research, information, and advocacy. Founded in 1940, the Assocation provides services to communities across the country. Its mission is to prevent and cure diabetes and to improve the lives of all people affected by diabetes.