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Getting the Right Diabetes Treatment

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What to Know About Prediabetes and Diabetes Tests

Medically Reviewed By Marina Basina, M.D.

Your medical team may use several tests to determine whether you have prediabetes or diabetes. Testing for diabetes often involves measuring blood sugar levels, such as after fasting or consuming a high-glucose drink. To diagnose diabetes, your doctor will ask about your symptoms, medical history, and family medical history. They may then recommend multiple tests and checkups.

Gestational diabetes is diabetes that develops during pregnancy. Doctors also recommend testing for gestational diabetes during pregnancy to determine if any treatment is necessary.

This article discusses the types of diabetes tests and what their results mean. It looks at tests to confirm diabetes type, diagnose gestational diabetes, and regularly monitor your health.

A1C test

Gloved hands holding up two vials of blood
Alvaro Lavin/Stocksy United

An A1C test measures your average blood sugar levels over the previous 3 months. It is also referred to as:

  • hemoglobin A1C test
  • HbA1C test
  • glycated hemoglobin or glycosylated hemoglobin test

A1C testing involves taking regular blood samples, such as by pricking the finger. There is no Trusted Source Centers for Disease Control and Prevention (CDC) Governmental authority Go to source special preparation required for A1C testing: You can eat and drink before the procedure.

Results

A1C test results are measured in percentages. The higher the percentage, the higher your average blood sugar level and diabetes risk.

Results for A1C testing include Trusted Source Centers for Disease Control and Prevention (CDC) Governmental authority Go to source :

PercentagePossible meaning
below 5.7%no diabetes
5.7–6.4%prediabetes
6.5% and abovediabetes

The diagnostic process can vary per person

Your medical team may repeat tests or use multiple test types to confirm your diagnosis. This is because not all tests are 100% accurate, or your doctors may want further confirmation.

Also, certain test results may not apply to people who are pregnant, as clinicians may use different thresholds. Read on to learn more about diabetes testing during pregnancy.

Fasting blood sugar test

A fasting blood sugar or blood glucose test measures your blood sugar levels after fasting. This means not eating or drinking anything other than water for a period of time, such as 8–10 hours.

Your doctor will instruct you how long to fast before having a blood sample drawn. They will also inform you of any other required preparation, such as avoiding smoking.

You may have to reschedule your blood test if you eat or drink anything other than water during the fasting period.

Results

Results for a fasting blood sugar test include Trusted Source Centers for Disease Control and Prevention (CDC) Governmental authority Go to source :

ResultsPossible meaning
99 milligrams per deciliter (mg/dL) or lowerno diabetes
100–125 mg/dL prediabetes
126 mg/dL or higherdiabetes

Glucose tolerance test

A glucose tolerance test measures your blood sugar levels before and after consuming a drink containing glucose. This may be a specifically formulated drink or a soft drink your medical team approves.

A glucose tolerance test involves the following steps:

  1. You will fast before the test for a period of time requested by your doctor.
  2. They will then take an initial blood sample to check your fasting blood sugar level.
  3. After this, your doctor will instruct you to drink a liquid containing glucose.
  4. Your doctor will take another blood sample 1–3 hours Trusted Source Centers for Disease Control and Prevention (CDC) Governmental authority Go to source after you consume the glucose drink.

A glucose tolerance test may also be referred to as an oral glucose tolerance test.

Results

Results of a glucose tolerance test include:

ResultsPossible meaning
140 mg/dL or lowertypical
140–199 mg/dLprediabetes
200 mg/dL or higherdiabetes

Random blood sugar test

A random blood sugar test checks your blood sugar levels at an unspecified time. You can schedule this test for any time Trusted Source Centers for Disease Control and Prevention (CDC) Governmental authority Go to source and do not have to fast beforehand.

Results

If the test shows your blood sugar level is 200 mg/dL or higher, you may have diabetes.

Tests to find the type of diabetes

The previous tests can tell you whether you have prediabetes or diabetes. However, they can’t tell you what type of diabetes you have.

As treatment varies per diabetes type, knowing which one you experience is important for effective care.

Tests for the type of diabetes include:

  • Autoantibodies test: Clinicians will take a blood sample for analysis in a lab. They will look for certain antibodies often found in people with type 1 diabetes.
  • Genetic testing for monogenic diabetes: Genetic testing involves taking a blood or saliva sample. Monogenic diabetes types are rare forms of diabetes that occur from changes in a single gene. By contrast, type 1 and type 2 diabetes are polygenic, involving changes in multiple genes. Monogenic diabetes accounts for around 1–4% of all diabetes cases.

Read more about type 1, type 2, and gestational diabetes.

Tests for gestational diabetes

The National Institutes of Health (NIH) recommends diabetes testing for everyone planning to become pregnant.

If you haven’t already received a diabetes diagnosis, your medical team may recommend testing within the first 15 weeks of your pregnancy. However, they may suggest earlier testing if you experience risk factors for gestational diabetes.

You may also have Trusted Source Centers for Disease Control and Prevention (CDC) Governmental authority Go to source type 1 or type 2 diabetes instead of gestational diabetes. This may be the case if your blood sugar levels are higher than typical early in your pregnancy.

Below are examples of tests for gestational diabetes:

Test typeProcedureResults
Glucose screening testA blood sample is taken 1 hour after consuming a glucose drink. You do not have to fast beforehand.Blood sugar levels of 140 mg/dL may prompt your doctor to order a glucose tolerance test.
Glucose tolerance testA blood sample is taken after fasting and again a few hours after consuming a glucose drink.

Results depend on the size of the glucose drink and your typical blood test results.

Ask your doctor for advice about your results.

Your doctor may also use other tests for gestational diabetes, such as an A1C test.

Tests and checkups after diagnosis

If you received a diagnosis of prediabetes or diabetes, your doctor may request regular checkups to monitor your condition. This can help them evaluate how you respond to treatment. They may also request regular monitoring if you have a high risk of diabetes. 

Checkups can involve repeating the same diagnostic tests. For example, the Centers for Disease Control and Prevention (CDC) Trusted Source Centers for Disease Control and Prevention (CDC) Governmental authority Go to source suggests having an A1C test at least twice a year if you have diabetes.

Without effective treatment, diabetes can lead to complications affecting multiple body systems. As a result, your doctor may also recommend other regular tests, such as:

  • blood pressure checks
  • cholesterol checks, known as a lipid panel or profile
  • foot exams
  • kidney function tests
  • eye exams
  • dental checkups

Read more about the possible complications of diabetes.

Summary

If your doctor suspects you have diabetes or prediabetes, they may order several tests to help with a diagnosis. These include A1C, fasting blood glucose, and glucose tolerance tests. They work by measuring the level of sugar in your blood using a blood sample.

Your doctor will give you instructions to prepare for your tests and help you interpret the results. Results may look different depending on the test.

Further tests can help identify your diabetes type and whether you may have gestational diabetes in pregnancy. Tests can also help monitor your health during regular checkups.

Contact your doctor if you have any questions.

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Medical Reviewer: Marina Basina, M.D.
Last Review Date: 2023 Sep 27
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