You’ll need to get your blood sugar tested to find out for sure if you have prediabetes or type 1, type 2, or gestational diabetes. Testing is simple, and results are usually available quickly.
Tests for Type 1 Diabetes, Type 2 Diabetes, and Prediabetes
Your doctor will have you take one or more of the following blood tests to confirm the diagnosis:
A1C Test
The A1C test measures your average blood sugar level over the past 2 or 3 months. An A1C below 5.7% is normal, between 5.7 and 6.4% indicates you have prediabetes, and 6.5% or higher indicates you have diabetes.
Fasting Blood Sugar Test
This measures your blood sugar after an overnight fast (not eating). A fasting blood sugar level of 99 mg/dL or lower is normal, 100 to 125 mg/dL indicates you have prediabetes, and 126 mg/dL or higher indicates you have diabetes.
Glucose Tolerance Test
This measures your blood sugar before and after you drink a liquid that contains glucose. You’ll fast (not eat) overnight before the test and have your blood drawn to determine your fasting blood sugar level. Then you’ll drink the liquid and have your blood sugar level checked 1 hour, 2 hours, and possibly 3 hours afterward. At 2 hours, a blood sugar level of 140 mg/dL or lower is considered normal, 140 to 199 mg/dL indicates you have prediabetes, and 200 mg/dL or higher indicates you have diabetes.
Random Blood Sugar Test
This measures your blood sugar at the time you’re tested. You can take this test at any time and don’t need to fast (not eat) first. A blood sugar level of 200 mg/dL or higher indicates you have diabetes.
Random Blood Sugar Test6.5% or above | 126 mg/dL or above | 200 mg/dL or above | 200 mg/dL or above |
5.7 – 6.4% | 100 – 125 mg/dL | 140 – 199 mg/dL | N/A |
Below 5.7% | 99 mg/dL or below | 140 mg/dL or below | N/A |
*Results for gestational diabetes can differ. Ask your health care provider what your results mean if you’re being tested for gestational diabetes.
Source: American Diabetes Association
If your doctor thinks you have type 1 diabetes, your blood may also tested for autoantibodies (substances that indicate your body is attacking itself) that are often present in type 1 diabetes but not in type 2 diabetes. You may have your urine tested for ketones (produced when your body burns fat for energy), which also indicate type 1 diabetes instead of type 2 diabetes.
Tests for Gestational Diabetes
Gestational diabetes is diagnosed using blood tests. You’ll probably be tested between 24 and 28 weeks of pregnancy. If your risk is higher for getting gestational diabetes (due to having more risk factors), your doctor may test you earlier. Blood sugar that’s higher than normal early in your pregnancy may indicate you have type 1 or type 2 diabetes rather than gestational diabetes.
Glucose Screening Test
This measures your blood sugar at the time you’re tested. You’ll drink a liquid that contains glucose, and then 1 hour later your blood will be drawn to check your blood sugar level. A normal result is 140 mg/dL or lower. If your level is higher than 140 mg/dL, you’ll need to take a glucose tolerance test.
Glucose Tolerance Test
This measures your blood sugar before and after you drink a liquid that contains glucose. You’ll fast (not eat) overnight before the test and have your blood drawn to determine your fasting blood sugar level. Then you’ll drink the liquid and have your blood sugar level checked 1 hour, 2 hours, and possibly 3 hours afterward. Results can differ depending on the size of the glucose drink and how often your blood sugar is tested. Ask your doctor what your test results mean.
Prevent Type 2 Diabetes
If your test results show you have prediabetes, ask your doctor or nurse if there is a lifestyle change program offered through the CDC-led National Diabetes Prevention Program in your community. You can also search for an online or in-person program. Having prediabetes puts you at greater risk for developing type 2 diabetes, but participating in the program can lower your risk by as much as 58% (71% if you’re over age 60).
Diabetes Treatment Plan
If your test results show you have type 1, type 2, or gestational diabetes, talk with your doctor or nurse about a detailed treatment plan—including diabetes self-management education and support services—and specific steps you can take to be your healthiest.
Test Quick Guide
The glucose tolerance test is a method to judge how well your body is able to metabolize glucose.
Glucose is the type of sugar your body uses to supply energy to its cells. Your body breaks down the food you eat into glucose that then enters your bloodstream. A hormone called insulin, made by your pancreas, helps bring the glucose from your bloodstream into the cells of your body.
If your body’s cells have difficulty accepting insulin, a condition called insulin resistance, or if your body cannot produce enough insulin, the glucose levels in your blood will be too high. High blood glucose can be a sign of prediabetes or diabetes. Diabetes is a serious medical issue that can damage the organs and tissues of the body if it is not controlled.
By measuring how your body processes glucose, the glucose tolerance test can be used with other tests to detect or confirm prediabetes and diabetes.
The glucose tolerance test is one
way to assess how well your body metabolizes glucose. Your doctor may have several different reasons for recommending this test: The glucose tolerance test measures the amount of glucose that remains in your bloodstream after fasting and then after drinking a sugary drink at fixed intervals. Blood glucose levels are typically measured in milligrams per deciliter, or mg/dL. Your doctor is typically the one to order a glucose tolerance test. The test may be conducted in your doctor’s office or in a hospital, clinic, or laboratory. There is no at-home glucose tolerance test at this time. This test requires several blood draws and laboratory analysis of blood samples, so it needs to be done in the setting of a clinic or
laboratory. A glucose tolerance test may cost different amounts depending on the type of health insurance you have and where the test is conducted. The full cost of the test may take into account the price of the office visit, the technician’s charges for obtaining your blood samples, and the fees for the laboratory to perform analysis on your samples. When your doctor orders a glucose tolerance test for
you, your insurance provider will usually cover the costs and fees associated with the test. You may need to cover some expenses out of pocket, such as deductibles and copayments. You can get more information about the cost of your glucose tolerance test by talking to your doctor, your health insurance company, or the staff at the office or facility where the test will be performed. When you receive a glucose tolerance test, a phlebotomist will draw a sample of your blood through a needle from a vein in your arm after you have fasted for at least eight hours, typically overnight. Then you will drink a sweet drink, and the technician will take more blood samples over the next two to three hours. You will be required to fast for at least eight hours before you take the test. This
means you will need to go without any food or any drink besides water. Since the test is often scheduled for the morning, most of your fasting can happen while you sleep the night before. You can generally follow a normal diet up until the time you begin fasting. Your doctor may ask you to make sure you consume at least 150 grams of carbohydrates each day in the three days before your glucose tolerance test. If you take any prescription medications or
over-the-counter drugs, be sure to discuss these with your doctor before you take the test. Your doctor can let you know whether any of these might alter the results of the test. They can also advise you whether you will need to stop taking any medications during the time you are fasting. To ensure the most reliable results, ask your doctor for any specific pretest preparations and carefully follow those instructions on the days leading up to your glucose tolerance test. Glucose tolerance testing usually takes place in the morning. You may need to stay at the testing site for up to three hours. The phlebotomist who gives you the test will start by drawing a small amount of your blood from a vein, most often in your arm. The technician may tie a band around your upper arm so the vein is easier to see. After cleaning the skin over your vein with a sterile wipe, a small needle will be
inserted through the skin and into the vein. The sample of blood goes into a tube attached to the needle. When the needle comes out, the phlebotomist will release the band on your arm and cover the injection site with a small bandage. Some people experience minor pain or discomfort when the needle goes in or comes out, but this usually does not last very long. Once the first blood sample is taken, you will drink a bottle of liquid containing a defined
amount of glucose. In adults, the drink usually contains 75 grams of glucose. In children, the amount is calculated based on body weight with a maximum of 75 grams. This drink tastes sweet like a sugary soda. After you drink the glucose solution, your blood will be drawn several more times at regular intervals over the next two or three hours. You should not eat anything during this time, and you typically will remain in the waiting area. After the series of blood draws is complete, you may experience slight pain where the blood was taken. You can generally resume normal activities after your glucose tolerance test is performed. When the test is completed, you will be able to eat again. You may wish to take a snack with you to the testing site to have on hand after your last blood draw is finished. You will usually get the results of your glucose tolerance test a few business days after you take the test. You may be able to access your test results online, or you may receive results by email or through postal mail. Your doctor may reach out by phone or email to discuss the test results or may schedule an appointment to go over the results in person. Laboratory technicians will analyze the glucose level in
each blood sample. Values for each of the separate timed samples will be included in your lab report.About the Test
Purpose of the test
What does the test measure?
Finding a Glucose
Tolerance Test
How to get tested
Can I take the test at home?
How much does the test cost?
Taking a Glucose
Tolerance Test
Before the test
During the test
After the
test
Receiving test results
Interpreting test results
The laboratory analysis will help determine if your glucose level in any of the blood samples is abnormally high. In particular, your blood glucose level measured two hours after you drink the glucose solution can be used in diagnosing diabetes or prediabetes.
The National Institute of Diabetes and Digestive and Kidney Disorders and the American Diabetes Association, among other organizations, list the following reference ranges for this two-hour value:
- Normal: Under 140 mg/dL
- Prediabetes: 140 to 199 mg/dL
- Diabetes: At or over 200 mg/dL
While this test can be used to diagnose both type 1 and type 2 diabetes, one test alone does not usually determine if you have diabetes. The doctor normally considers whether you have symptoms of diabetes, the results of other blood tests, or a repeated glucose tolerance test to arrive at a definitive diagnosis.
As a result, the best way to understand what your glucose tolerance test results mean is to discuss them with your doctor. Your doctor can explain how your results compare to the reference ranges, whether you will need a repeat test or other follow-up tests, and what further steps you may need to take for your health.
People diagnosed with prediabetes have a greater risk of developing diabetes and other health conditions over the years following their diagnosis. If your test results indicate prediabetes, your doctor may recommend dietary and lifestyle changes that can lower the chance that your condition will progress to diabetes or that can delay this progression.
If you are diagnosed with diabetes, your doctor may go over the steps you need to take to manage your condition. These steps can include monitoring your blood glucose at home and changing your diet and exercise routine. Your doctor may also prescribe medication and regular follow-up visits.
- Hemoglobin A1c Learn More
- Glucose Tests for Gestational Diabetes Learn More
- Glucose Testing Learn More
- American Diabetes Association Learn More
- National Institute of Diabetes and Digestive and Kidney Diseases Learn More
- CDC: Diabetes Learn More
Sources
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American Diabetes Association. Classification and diagnosis of diabetes. Diabetes Care. 2020; 43(Supplement 1): S14-S31. doi: 10.2337/dc20-S002
ARUP Consult. Diabetes mellitus. Updated May 2021. Accessed June 3, 2021. //arupconsult.com/content/diabetes-mellitus
Brutsaert E. Diabetes mellitus (DM). Merck Manuals Consumer Edition. Updated September 2020. Accessed June 3, 2021. //www.merckmanuals.com/home/hormonal-and-metabolic-disorders/diabetes-mellitus-dm-and-disorders-of-blood-sugar-metabolism/diabetes-mellitus-dm
Brutsaert E. Diabetes mellitus (DM). Merck Manuals Professional Edition. Updated September 2020. Accessed June 3, 2021. //www.merckmanuals.com/professional/endocrine-and-metabolic-disorders/diabetes-mellitus-and-disorders-of-carbohydrate-metabolism/diabetes-mellitus-dm
Centers for Disease Control and Prevention. Diabetes tests. Updated May 15, 2019. Accessed June 3, 2021. //www.cdc.gov/diabetes/basics/getting-tested.html
Centers for Disease Control and Prevention. What is diabetes? Updated June 11, 2020. Accessed June 3, 2021. //www.cdc.gov/diabetes/basics/diabetes.html
Hayward RA, Selvin E. Screening for type 2 diabetes mellitus. In: Elmore JG, Nathan DM, eds. UpToDate. Updated May 4, 2021. Accessed June 3, 2021. //www.uptodate.com/contents/screening-for-type-2-diabetes-mellitus
Inzzucchi SE, Lupsa B. Clinical presentation, diagnosis, and initial evaluation of diabetes mellitus in adults. In: Nathan DM, Wolfsdorf JI, eds. UpToDate. Updated April 28, 2021. Accessed June 3, 2021. //www.uptodate.com/contents/clinical-presentation-diagnosis-and-initial-evaluation-of-diabetes-mellitus-in-adults
Laffel L, Svoren B. Epidemiology, presentation, and diagnosis of type 2 diabetes mellitus in children and adolescents. In: Wolfsdorf JI, ed. UpToDate. Updated September 30, 2020. Accessed June 6, 2021. //www.uptodate.com/contents/epidemiology-presentation-and-diagnosis-of-type-2-diabetes-mellitus-in-children-and-adolescents
Lin JJ. Glucose tolerance testing. Deveraj S, ed. Medscape. Updated: May 13, 2021. Accessed June 3, 2021. //emedicine.medscape.com/article/2049402-overview#a1
MedlinePlus: National Library of Medicine. Blood glucose test. Updated July 30, 2020. Accessed June 3, 2021. //medlineplus.gov/lab-tests/blood-glucose-test/
MedlinePlus: National Library of Medicine. Fasting for a blood test. Updated March 3, 2021. Accessed June 6, 2021. //medlineplus.gov/lab-tests/fasting-for-a-blood-test/
MedlinePlus: National Library of Medicine. Venipuncture. Updated April 21, 2019. Accessed May 25, 2021. //medlineplus.gov/ency/article/003423.htm
National Heart, Lung, and Blood Institute. Blood tests. Date unknown. Accessed June 6, 2021. //www.nhlbi.nih.gov/health-topics/blood-tests
National Institute of Diabetes and Digestive and Kidney Diseases. Diabetes & prediabetes tests. Updated August 2020. Accessed June 3, 2021. //www.niddk.nih.gov/health-information/professionals/clinical-tools-patient-management/diabetes/diabetes-prediabetes
National Institute of Diabetes and Digestive and Kidney Diseases. Diabetes tests & diagnosis. Updated December 2016. Accessed June 3, 2021. //www.niddk.nih.gov/health-information/diabetes/overview/tests-diagnosis#diagnosediabetes
National Institute of Diabetes and Digestive and Kidney Diseases. Insulin resistance and prediabetes. Updated May 2018. Accessed June 3, 2021. //www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes/prediabetes-insulin-resistance
National Institute of Diabetes and Digestive and Kidney Diseases. What is diabetes? Updated December 2016. Accessed June 3, 2021. //www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes
U.S. Preventive Services Task Force. Screening for Abnormal Blood Glucose and Type 2 Diabetes Mellitus: U.S. Preventive Services Task Force Recommendation Statement. Update October 26, 2015. Accessed November 4, 2021. //www.acpjournals.org/doi/full/10.7326/M15-2345?rfr_dat=cr_pub++0pubmed&url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org
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