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Diabetes Tests

What Is Diabetes?

Diabetes is a condition that affects the body’s ability to either produce or use insulin. Insulin helps the body utilize blood sugar for energy. Diabetes results in blood sugar levels (blood glucose) to rise to abnormally high levels.  Diabetes results in damage to blood vessels and nerves, causing difficulty seeing, tingling and numbness in the hands and feet, and increased risk for experiencing a heart attack of stroke.

Diagnosing diabetes as quickly as possible means patients can start treating diabetes and taking steps to live a healthier lifestyle.

Who Should Undergo Diabetes Testing?

In its early stages, diabetes may not cause many symptoms. However, some people experience symptoms that include:

  • sudden weight loss
  • extreme thirst
  • feeling tired all the time
  • feeling very hungry, even after eating
  • difficulty seeing
  • urinating more often than usual

Other people should be tested for diabetes, even if they are not experiencing symptoms. The American Diabetes Association (ADA) recommends the following people undergo diabetes testing:

  • anyone with a body mass index greater than 25
  • patients with high blood pressure, high cholesterol, or heart disease
  • people who have a family history of diabetes
  • those who do not engage in regular physical activity
  • women with a history of polycystic ovary syndrome (PCOS)

The ADA also recommends anyone who is older than age 45 undergo an initial blood sugar test. This helps a person establish a baseline for blood sugar levels. Because a person’s risk for getting diabetes increases with age, testing can help people identify their risks.

Blood Testing for Diabetes

A1C Test

Blood testing allows a doctor to determine the levels of blood sugar in the body. The A1C test is one of the most common tests because its results measure blood sugar levels over time. Also known as the glycated hemoglobin test, the test measures how much glucose has attached itself to red blood cells in the body over the last three months.

Red blood cells have a lifespan of about three months. Because the A1C test examines blood glucose, it measures a person’s average blood sugar for roughly three months. The test requires gathering only a small amount of blood. The results are measured in a percentage:

  • less than 5.7 percent: normal reading
  • between 5.7 and 6.4 percent: prediabetes
  • greater than 6.5 percent: diabetes

While doctors can perform these tests in-office to receive immediate results, these aren’t considered to be as accurate as tests sent to a laboratory. Lab tests are standardized. This means that no matter the lab performing the test, the methods to test the blood are the same. According to the National Diabetes Information Clearinghouse, only tests from a laboratory should be considered definitive enough to diagnose diabetes. 

Some people may have varied results using the A1C test. This includes pregnant women or people with a special hemoglobin variant that makes the test results inaccurate. A doctor may suggest alternate diabetes tests in these circumstances.

Random Blood Sugar Test

A random blood sugar test involves drawing blood at any given time, no matter when you last ate. If the result is higher than 200 milligrams per deciliter (mg/dL) this could indicate diabetes.  

Fasting Blood Sugar Test

Fasting blood sugar tests involve drawing blood after a person has not eaten overnight. Results less than 100 mg/dL are normal. Results between 100 to 125 mg/dL are considered prediabetes. Results greater than 126 mg/dL after two tests are considered diagnostic for diabetes.

Oral Glucose Tolerance Test

The oral glucose test (OGTT) is a test that takes place over the course of two hours. A person’s blood sugar is tested initially and then given a sugary drink. After two hours, blood sugar levels are tested again. The results are:

  • less than 140 mg/dL: normal
  • between 140 and 199 mg/dL: prediabetes
  • greater than 200 mg/dL: diabetes

Urine Testing for Diabetes

Urine tests aren’t used to definitively diagnose diabetes. However, they are often used when doctor thinks the patient may have type 1 diabetes. Laboratories can test urine for ketone bodies. The body produces ketone bodies when fat tissue is used for energy instead of blood sugar. If ketone bodies are in the urine, this could indicate the person isn’t making enough insulin.

Gestational Diabetes Tests

Gestational diabetes can occur when a woman is pregnant. Women are tested early in a pregnancy if they have a family history of gestational diabetes or have had it before. Women who don’t have these risk factors are tested in the second trimester instead.

Doctors may use two different test types to diagnose gestational diabetes. The first is an initial glucose challenge test. This test involves drinking a glucose syrup solution. Blood is drawn after an hour to measure blood sugar levels. A result of 140 mg/dL or less is considered normal. A higher-than-usual reading indicates the need for further testing.

The follow-up glucose tolerance testing involves not eating anything overnight. An initial blood sugar level is measured. The expectant mom will then drink a high-sugar solution. The blood sugar is then checked hourly for three hours. If a woman has two or more higher-than-usual readings, the results indicate gestational diabetes. 

Content licensed from:

Written by: Rachel Nall, RN, BSN
Published on: Oct 09, 2014
Medically reviewed on: Nov 30, 2016: 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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