A Guide to Diabetes Testing

There are many scenarios in which your doctor would recommend a diabetes screening or blood sugar testing. You may feel tired, thirsty, or have other symptoms of diabetes. Screening for gestational diabetes is common for pregnant women during their second trimester. And if you have a family history of diabetes, your doctor may want to check your blood sugar levels during your physical.

There are several ways that doctors can test for diabetes. The good news is that testing is quite simple, and usually some blood and potentially some fasting. And — surprise! — you’ve likely already taken a diabetes screening test. Routine blood tests include some of the most common diabetes screens.

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How Doctors Test for Diabetes

Diabetes is a disease that leads to abnormal blood glucose levels. Glucose is a type of sugar used as an essential energy source in the body. Our digestive system makes glucose from our food, which our body uses as fuel.

In diabetes, the body’s metabolism systems start to malfunction. That can lead to too much or too little glucose in your blood. When that happens, your cells can’t make the energy they need to work their best. This malfunction can lead to a wide variety of medical problems.

There are several different tests your doctor may order to check for Type 1, Type 2, or gestational diabetes. Most of them test your blood glucose levels in some capacity.

Blood glucose test

One of the most common is the random glucose test. This test is a spot-check for your blood glucose level. It’s usually done as part of a routine blood panel to check your cholesterol, blood counts, and vitamin levels. This test measures the amount of glucose circulating in the blood.

  • Even after eating, most people’s glucose levels are 125 milligrams per deciliter (mg/dL) or less.
  • If a test comes back with glucose levels of 200 mg/dL or higher, it’s a sign of diabetes. If you also have symptoms, blood glucose of 200 mg/dL or more is enough for a diabetes diagnosis.

Hemoglobin A1C (HBA1C) blood test

Another standard screening for diabetes is the hemoglobin A1C (HBA1C) blood test. HBA1C doesn’t take a one-time snapshot of your glucose levels. Instead, this test shows how high or low your blood sugar has been over three months.

  • Healthy individuals will have a reading of less than 5.6%.
  • Those with prediabetes will be in the 5.7% to 6.4% range.
  • Anything higher than 6.5% is in the diabetic range.

Fasting glucose test

If your blood glucose levels, HBA1C, or other symptoms suggest diabetes, your doctor may ask you to do a fasting glucose test. High glucose levels in your blood when you haven’t eaten can be a sign of diabetes. Your doctor will want you to abstain from eating (fast) for 8-12 hours before getting your blood glucose tested.

  • A reading of 126 mg/dL or higher indicates you may have diabetes.

Glucose challenge test

When your doctor suspects diabetes, they may also want to do a glucose challenge. The glucose challenge is the type of test that most pregnant women take to screen for gestational diabetes. Nearly 10% of pregnant women in the United States develop insulin resistance during their pregnancies, according to the American Diabetes Association.

You can eat and drink normally before the glucose challenge. Then, you’ll drink a sugary drink containing 50 grams of glucose. You’ll have your blood drawn one hour later to test the blood glucose levels.

  • If your blood glucose is 140 mg/dL or higher, they’ll have you do a glucose tolerance test.

Glucose tolerance test

For a glucose tolerance test, you’ll first fast overnight. You’ll then have blood drawn to measure your blood sugars before drinking the glucose solution. The glucose tolerance test solution for pregnant women contains 75 grams of glucose.

After the fasting blood draw, you’ll wait for at least one hour. The nurse will draw blood and test it for blood sugar levels at one, two and three hours later.

For the three-hour glucose tolerance test for gestational diabetes. If any two of these are abnormal, you’ll be diagnosed with gestational diabetes:

  • Your fasting blood glucose levels should be under 95 mg/dL.
  • At one hour, your blood glucose should be under 180 mg/dL.
  • At two hours, blood sugars should be under 155 mg/dL.
  • At three hours, blood glucose should be under 140 mg/dL.

Tests for Getting to the Right Diagnosis

Your doctor can determine if you have Type 1 or Type 2 diabetes depending on your age, symptoms, and response to treatment.

Generally speaking, Type 1 diabetes develops swiftly — and experiences more pronounced symptoms. Type 2 diabetes, on the other hand, has a slower progression. Gestational diabetes only develops during pregnancy and resolves after birth.

If your doctor suspects Type 1 diabetes, they may order more tests. Some tests measure signals that indicate an autoimmune disease. These signals include islet cell antibodies or insulin autoantibodies.

The doctor may also test your urine for ketones. The liver produces these compounds when the body burns fat instead of carbs for energy.

It is also likely that your doctor will want to repeat one or all of the different diabetic tests. They’ll want to confirm the diagnosis and track your health. Lifestyle changes and medications can help improve blood glucose numbers and HBA1C.

In keeping tabs on these numbers, you and your doctor will be in a better position to develop an effective management plan. Over time, improvement in these numbers helps ensure your management plan is working.

American Diabetes Association. Diagnosis. Link.

Centers for Disease Control. Diabetes Tests. Link.

Centers for Disease Control. All About Your A1C. Link.

Juvenile Diabetes Research Fund. The Complexity of Diagnosing Type 1 Diabetes. Link.

American Diabetes Association. Gestational diabetes and a healthy baby? Yes. Link.

NIH National Library of Medicine. Glucose screening tests during pregnancy. Link.

NIH National Library of Medicine. Glucose tolerance test - non-pregnant. Link.

About Endocrinology

The UPMC Department of Endocrinology stands as a national leader in research of diabetes and endocrine conditions. We partner with the University of Pittsburgh Division of Endocrinology and Metabolism for research and clinical trials. We treat diabetes, obesity, osteoporosis, hormonal disorders, and thyroid disorders at several locations across our communities. We also have specialized Diabetes Centers to help you manage your disease. Find an expert near you.