By Rachel Nall, MSN, CRNA

Reviewed by Deborah Weatherspoon, PhD, RN, CRNA

It can take time for the symptoms of diabetes to appear. However, a doctor may be able to detect the condition in its earlier stages by performing various medical tests.

These tests can detect different forms of diabetes, including type 1, type 2, and gestational diabetes.

In this article, we describe the types of diabetes and the tests that detect them, including their processes and results. We also cover home testing kits and when to see a doctor.

Type 2

Doctors can use several different tests to detect type 2 diabetes. In a person with this condition, the body produces insulin but is unable to use it effectively.

Hemoglobin A1c

One of the most common diabetes tests is the A1c test.

The doctor may also refer to this as the hemoglobin A1c, HbA1c, or glycated hemoglobin test. It measures the attachment of glucose (blood sugar) molecules to hemoglobin, which is a component of red blood cells.

The A1c test results indicate a person’s average blood sugar level over 3 months. If this level is higher than 5.7%, it shows that there is a consistent, unusually high amount of glucose in the blood, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

A person does not have to fast before this test, which just involves taking a small blood sample.

A doctor may diagnose diabetes based on the results of an A1c test alone. However, the only form of diabetes that it can detect is type 2 diabetes.

Fasting plasma glucose test

The fasting plasma glucose (FPG) test requires a person to have no food or drink for 8 hours before giving a blood sample. The doctor’s office tends to schedule it early in the morning, and the test usually involves taking blood either from a finger, which some healthcare professionals call a “finger-stick test,” or from a vein in the arm.

Random plasma glucose test

A random plasma glucose (RPG) test also tends to involve a finger stick or taking blood from an arm vein. The major difference between this test and an FPG test is that an RPG test does not require the person to fast in preparation.

Type 1

Type 1 diabetes can be difficult to diagnose. It develops when the body does not produce enough insulin, a hormone that it needs to process blood sugar.

Without treatment, type 1 diabetes can cause a person’s blood sugar levels to rise very high. Treatment involves injecting insulin.

If a doctor suspects type 1 diabetes, they will check whether a person is experiencing its symptoms, which can include extreme fatigue and flu-like symptoms.

The doctor can also use the following tests:

• FPG: This blood test indicates how well the body is processing glucose.
• Oral glucose tolerance test: For this test, a person will need to fast and then drink a solution that contains glucose. A healthcare professional will then measure blood sugar levels every hour for 2–3 hours.
• A1c: This test can indicate average blood sugar levels over the past 3 months, but the results can be incorrectly low in people with type 1 diabetes.

If the results are inconclusive, the doctor may order any of the following tests:

• C-peptide: The pancreas produces this protein alongside insulin. Low levels of C-peptide in the blood can suggest low levels of insulin.
• Insulin autoantibodies: This test checks for the presence of proteins that target and destroy insulin.
• Glutamic acid decarboxylase autoantibodies: Doctors use this test to check for the presence of antibodies that can destroy enzymes in insulin-producing cells.
• Insulinoma-associated 2 autoantibodies: The presence of these antibodies can also indicate that the body is attacking the cells that produce insulin.
• Islet cell cytoplasmic autoantibodies: The Juvenile Diabetes Research Foundation estimate that 80% of people with type 1 diabetes have this type of antibody.
• Zinc transport 8: This test identifies antibodies that kill insulin-producing beta cells.

A doctor may only be able to make a conclusive diagnosis after seeing the results of several of these tests.

Gestational diabetes

Doctors typically use two tests to diagnose gestational diabetes, which develops in pregnant women.

Glucose challenge test

A doctor typically performs this test between 24 and 28 weeks of pregnancy, according to the NIDDK. It is usually the first test for gestational diabetes.

The glucose challenge test requires a person to drink a beverage that contains glucose. An hour later, a healthcare professional will draw blood to measure the level of glucose.

A result of 135 milligrams per deciliter (mg/dl) or higher may indicate that the body is not processing glucose correctly.

To confirm a diagnosis of gestational diabetes, the doctor will recommend an oral glucose tolerance test.

Oral glucose tolerance test

This test requires the woman to fast for 8 hours and then give a blood sample. Next, she will drink something that contains glucose, and a healthcare professional will draw blood once an hour for at least 2 hours.

If blood sugar levels remain high throughout this period, this can indicate gestational diabetes.

Home testing

Some tests are possible for people to carry out themselves at home. These include:

Blood sugar testing

Home testing kits can measure blood sugar. The specific components of the kits vary, but most include:

• lancets for pricking the finger
• test strips to collect the blood
• a machine called a glucometer that evaluates the sample and gives a reading

A doctor will determine a person’s target blood sugar levels, and they will also explain which results indicate the need for medical attention.

Urine ketone testing

A different type of home test evaluates the urine for the presence of ketones, which the body produces by breaking down fats for energy. Ketones usually indicate that the body has too little insulin.

Most pharmacies sell these kits. The test involves collecting a urine sample, then inserting the provided strips into the urine. These will indicate the presence of ketones.

If ketone levels are moderate or high, a person should usually seek medical attention.

Results

According to NIDDK, the following are the general ranges of diabetes test results. The doctors may use these ranges when considering a diabetes diagnosis.

A1c

• normal: less than 5.7%
• prediabetes: 5.7–6.4%
• diabetes: 6.5% or higher

FPG

• normal: 99 mg/dl or under
• prediabetes: 100–125 mg/dl
• diabetes: 126 mg/dl or higher

RPG

When levels are 200 mg/dl or higher, a person could have diabetes.

Summary

A doctor or trained diabetes educator can provide more information about the tests and their purposes.

Most are blood tests, although a urine ketone test can also indicate whether the body has enough insulin.

Following a diagnosis, the doctor may use some of these tests to track the effectiveness of a person’s diabetes care plan.