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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, or blood glucose, that rises to abnormally high levels. Over time, diabetes results in damage to blood vessels and nerves, causing a variety of symptoms, including:

  • difficulty seeing
  • tingling and numbness in the hands and feet
  • increased risk for a heart attack or stroke

An early diagnosis means you can start treatment and take steps toward a healthier lifestyle.

Who should undergo diabetes testing?

In its early stages, diabetes may or may not cause many symptoms. You should get tested if you experience any of the early symptoms that do sometimes occur, including:

  • extreme thirst
  • feeling tired all the time
  • feeling very hungry, even after eating
  • blurry vision
  • urinating more often than usual
  • have sores or cuts that won’t heal

Some people should be tested for diabetes even if they aren’t experiencing symptoms. The American Diabetes Association (ADA) recommends you undergo diabetes testing if you’re overweight (body mass index greater than 25) and fall into any of the following categories:

  • you’re a high risk ethnicity (African American, Latino, Native American, Pacific Islander, Asian American)
  • you have high blood pressure, high triglycerides, low HDL cholesterol, or heart disease
  • you have a family history of diabetes
  • you have a personal history of abnormal blood sugar levels or signs of insulin resistance
  • you don’t engage in regular physical activity
  • you’re a woman with a history of polycystic ovary syndrome (PCOS) or gestational diabetes

The ADA also recommends you undergo an initial blood sugar test if you are over the age of 45. This helps you establish a baseline for blood sugar levels. Because your risk for diabetes increases with age, testing can help you identify your chances for developing it.

Blood tests 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 because its results estimate blood sugar levels over time, and you don’t have to fast. The test is also known as the glycated hemoglobin test. It measures how much glucose has attached itself to red blood cells in your body over the last two to three months.

Since red blood cells have a lifespan of about three months, the A1C test measures your average blood sugar for about 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
  • equal to or greater than 6.5 percent: diabetes

Lab tests are standardized by the National Glycohemoglobin Standardization Program (NGSP). This means that no matter what lab performs the test, the methods to test the blood are the same. According to the National Institute of Diabetes and Digestive and Kidney Diseases, only tests that have been approved by the NGSP 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. Your 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 equal to or higher than 200 milligrams per deciliter (mg/dL) this could indicate diabetes. Results in the 140-199 mg/dL range can indicate prediabetes.

Fasting blood sugar test

Fasting blood sugar tests involve drawing blood after you have not eaten overnight, usually for 8 to 12 hours. Results less than 100 mg/dL are normal. Results between 100 to 125 mg/dL are considered prediabetes. Results equal to or 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 diagnose diabetes. Doctors often use them if they think you 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 present in moderate to large amounts in the urine, this could indicate your body is not 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.

The second test involves doing a two hour glucose tolerance test, similar to the one described above. One out-of-range value would be diagnostic for gestational diabetes using this test.

Content licensed from:

Written by: Rachel Nall, RN, BSN
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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