Blood sugar test – blood

[2] American Diabetes Association. Standards of medical care in diabetes—2017. Diabetes Care. 2017;40(Suppl 1).

Insulin Resistance and Prediabetes

Insulin resistance and prediabetes occur when your body doesn’t use insulin well.

What is insulin?

Insulin is a hormone made by the pancreas that helps glucose in your blood enter cells in your muscle, fat, and liver, where it’s used for energy. Glucose comes from the food you eat. The liver also makes glucose in times of need, such as when you’re fasting. When blood glucose, also called blood sugar, levels rise after you eat, your pancreas releases insulin into the blood. Insulin then lowers blood glucose to keep it in the normal range.

What is insulin resistance?

Insulin resistance is when cells in your muscles, fat, and liver don’t respond well to insulin and can’t easily take up glucose from your blood. As a result, your pancreas makes more insulin to help glucose enter your cells. As long as your pancreas can make enough insulin to overcome your cells’ weak response to insulin, your blood glucose levels will stay in the healthy range.

What is prediabetes?

Prediabetes means your blood glucose levels are higher than normal but not high enough to be diagnosed as diabetes. Prediabetes usually occurs in people who already have some insulin resistance or whose beta cells in the pancreas aren’t making enough insulin to keep blood glucose in the normal range. Without enough insulin, extra glucose stays in your bloodstream rather than entering your cells. Over time, you could develop type 2 diabetes.

How common is prediabetes?

More than 84 million people ages 18 and older have prediabetes in the United States. 1 That’s about 1 out of every 3 adults.

Who is more likely to develop insulin resistance or prediabetes?

People who have genetic or lifestyle risk factors are more likely to develop insulin resistance or prediabetes. Risk factors include

• overweight or obesity
• age 45 or older
• a parent, brother, or sister with diabetes
• African American, Alaska Native, American Indian, Asian American, Hispanic/Latino, Native Hawaiian, or Pacific Islander American ethnicity
• physical inactivity
• health conditions such as high blood pressure and abnormal cholesterol levels
• a history of gestational diabetes
• a history of heart disease or stroke
• polycystic ovary syndrome, also called PCOS

People who have metabolic syndrome—a combination of high blood pressure, abnormal cholesterol levels, and large waist size—are more likely to have prediabetes.

Along with these risk factors, other things that may contribute to insulin resistance include

• certain medicines, such as glucocorticoids, some antipsychotics, and some medicines for HIV
• hormonal disorders, such as Cushing’s syndrome and acromegaly
• sleep problems, especially sleep apnea

Although you can’t change risk factors such as family history, age, or ethnicity, you can change lifestyle risk factors around eating, physical activity, and weight. These lifestyle changes can lower your chances of developing insulin resistance or prediabetes.

Being overweight or having obesity are risk factors for developing insulin resistance or prediabetes.

What causes insulin resistance and prediabetes?

Researchers don’t fully understand what causes insulin resistance and prediabetes, but they think excess weight and lack of physical activity are major factors.

Excess weight

Experts believe obesity, especially too much fat in the abdomen and around the organs, called visceral fat, is a main cause of insulin resistance. A waist measurement of 40 inches or more for men and 35 inches or more for women is linked to insulin resistance. This is true even if your body mass index (BMI) falls within the normal range. However, research has shown that Asian Americans may have an increased risk for insulin resistance even without a high BMI.

Researchers used to think that fat tissue was only for energy storage. However, studies have shown that belly fat makes hormones and other substances that can contribute to chronic, or long-lasting, inflammation in the body. Inflammation may play a role in insulin resistance, type 2 diabetes, and cardiovascular disease.

Excess weight may lead to insulin resistance, which in turn may play a part in the development of fatty liver disease.

Physical inactivity

Not getting enough physical activity is linked to insulin resistance and prediabetes. Regular physical activity causes changes in your body that make it better able to keep your blood glucose levels in balance.

What are the symptoms of insulin resistance and prediabetes?

Insulin resistance and prediabetes usually have no symptoms. Some people with prediabetes may have darkened skin in the armpit or on the back and sides of the neck, a condition called acanthosis nigricans. Many small skin growths called skin tags often appear in these same areas.

Even though blood glucose levels are not high enough to cause symptoms for most people, a few research studies have shown that some people with prediabetes may already have early changes in their eyes that can lead to retinopathy. This problem more often occurs in people with diabetes.

How do doctors diagnose insulin resistance and prediabetes?

Doctors use blood tests to find out if someone has prediabetes, but they don’t usually test for insulin resistance. The most accurate test for insulin resistance is complicated and used mostly for research.

Doctors use blood tests to find out if someone has prediabetes.

Doctors most often use the fasting plasma glucose (FPG) test or the A1C test to diagnose prediabetes. Less often, doctors use the oral glucose tolerance test (OGTT), which is more expensive and not as easy to give.

The A1C test reflects your average blood glucose over the past 3 months. The FPG and OGTT show your blood glucose level at the time of the test. The A1C test is not as sensitive as the other tests. In some people, it may miss prediabetes that the OGTT could catch. The OGTT can identify how your body handles glucose after a meal—often before your fasting blood glucose level becomes abnormal. Often doctors use the OGTT to check for gestational diabetes, a type of diabetes that develops during pregnancy.

People with prediabetes have up to a 50 percent chance of developing diabetes over the next 5 to 10 years. You can take steps to manage your prediabetes and prevent type 2 diabetes.

The following test results show Prediabetes 2

• A1C—5.7 to 6.4 percent
• FPG—100 to 125 mg/dL (milligrams per deciliter)
• OGTT—140 to 199 mg/dL

You should be tested for prediabetes if you are overweight or have obesity and have one or more other risk factors for diabetes, or if your parents, siblings, or children have type 2 diabetes. Even if you don’t have risk factors, you should start getting tested once you reach age 45.

If the results are normal but you have other risk factors for diabetes, you should be retested at least every 3 years. 2

How can I prevent or reverse insulin resistance and prediabetes?

Physical activity and losing weight if you need to may help your body respond better to insulin. Taking small steps, such as eating healthier foods and moving more to lose weight, can help reverse insulin resistance and prevent or delay type 2 diabetes in people with prediabetes.

Physical activity can help prevent or reverse insulin resistance and prediabetes.

The National Institutes of Health-funded research study, the Diabetes Prevention Program (DPP), showed that for people at high risk of developing diabetes, losing 5 to 7 percent of their starting weight helped reduce their chance of developing the disease. 3 That’s 10 to 14 pounds for someone who weighs 200 pounds. People in the study lost weight by changing their diet and being more physically active.

The DPP also showed that taking metformin, a medicine used to treat diabetes, could delay diabetes. Metformin worked best for women with a history of gestational diabetes, younger adults, and people with obesity. Ask your doctor if metformin might be right for you.

Making a plan, tracking your progress, and getting support from your health care professional, family, and friends can help you make lifestyle changes that may prevent or reverse insulin resistance and prediabetes. You may be able to take part in a lifestyle change program as part of the National Diabetes Prevention Program.

Clinical Trials

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) and other components of the National Institutes of Health (NIH) conduct and support research into many diseases and conditions.

What are clinical trials, and are they right for you?

Clinical trials are part of clinical research and at the heart of all medical advances. Clinical trials look at new ways to prevent, detect, or treat disease. Researchers also use clinical trials to look at other aspects of care, such as improving the quality of life for people with chronic illnesses. Find out if clinical trials are right for you.

What clinical trials are open?

Clinical trials that are currently open and are recruiting can be viewed at www.ClinicalTrials.gov.

References

[1] National Diabetes Statistics Report, 2017. Centers for Disease Control and Prevention website. https://www.cdc.gov/diabetes/php/data-research/index.html. Updated July 17, 2017. Accessed October 19, 2017.

[2] American Diabetes Association. Standards of medical care in diabetes—2017. Diabetes Care. 2017;40(Suppl 1).

[3] Diabetes Prevention Program Research Group. Long-term effects of lifestyle intervention or metformin on diabetes development and microvascular complications over 15-year follow-up: the Diabetes Prevention Program Outcomes Study. The Lancet: Diabetes and Endocrinology. 2015;3(11):866‒875.

Last Reviewed May 2018
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This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. NIDDK translates and disseminates research findings to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by NIDDK is carefully reviewed by NIDDK scientists and other experts.

The NIDDK would like to thank Rita Basu, M.D., University of Virginia School of Medicine

Blood sugar test – blood

A blood sugar test measures the amount of a sugar called glucose in a sample of your blood. Glucose is a major source of energy for most cells of the body, including brain cells. Glucose is a building block for carbohydrates. Carbohydrates are found in fruit, cereal, bread, pasta, and rice. Carbohydrates are quickly turned into glucose in your body. This can raise your blood glucose level. The hormone insulin made in the body helps control the blood glucose level.

Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. Preparation may vary depending on the specific test.

How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

• After you have not eaten anything for at least 8 hours (fasting)
• At any time of the day (random)
• Two hours after you drink a certain amount of glucose (2 hour post-prandial glucose test or oral glucose tolerance test)

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

Why the Test is Performed

Your health care provider may order this test if you have signs of diabetes. More than likely, the provider will order a fasting blood sugar test.

The blood glucose test is also used to monitor people who already have diabetes.

The test may also be done if you have:

• An increase in how often you need to urinate
• Recently gained a lot of weight
• Blurred vision
• Confusion or a change in the way you normally talk or behave
• Fainting spells
• Seizures (for the first time)
• Unconsciousness or coma

SCREENING FOR DIABETES

This test may also be used to screen a person for diabetes.

High blood sugar and diabetes may not cause symptoms in the early stages. A fasting blood sugar test is the most common test done to screen for diabetes, usually starting at age 35. If you have no other diabetes risk factors, you should be tested every 3 years (in some cases, more often if your weight is rising).

If you’re overweight and have any of the other risk factors below, ask your provider about getting tested at an earlier age and more often:

• High blood sugar level on a previous test
• Blood pressure of 140/90 mm Hg or higher, or unhealthy cholesterol levels
• History of heart disease
• Member of a high-risk ethnic group (African American, Latino, Native American, Asian American, or Pacific Islander)
• Woman who has been previously diagnosed with gestational diabetes
• Polycystic ovary disease (condition in which a woman has an imbalance of female sex hormones which may cause cysts in the ovaries)
• Close relative with diabetes (such as a parent, brother, or sister)
• Not physically active

Children age 10 and older who are overweight and have at least two of the risk factors listed above should be tested for type 2 diabetes every 3 years, even if they have no symptoms.

In 2022, the US Preventive Services Task Force concluded that there was not enough evidence to recommend screening for type 2 diabetes in people 18 years old or younger. Some experts do advocate such screening for overweight children. Ask your child’s provider what is best for them.

Normal Results

If you had a fasting blood glucose test, a level of 70 to 99 mg/dL (3.9 and 5.5 mmol/L) is considered normal.

If you had a random blood glucose test, a normal result depends on when you last ate. Most of the time, the blood glucose level will be 125 mg/dL (6.9 mmol/L) or lower.

The examples above show the common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different specimens. Talk to your provider about the meaning of your specific test results.

Blood glucose measured by a blood test from a vein is considered more accurate than blood glucose measured from a fingerstick with a blood glucose meter, or blood glucose measured by a continuous glucose monitor.

What Abnormal Results Mean

If you had a fasting blood glucose test:

• A level of 100 to 125 mg/dL (5.6 to 6.9 mmol/L) means you have impaired fasting glucose, a type of prediabetes. This increases your risk of developing type 2 diabetes and you should consult with your provider.
• A level of 126 mg/dL (7 mmol/L) or higher usually means you have diabetes.

If you had a random blood glucose test:

• A level of 200 mg/dL (11 mmol/L) or higher often means you have diabetes.
• Your provider will order a fasting blood glucose, A1C test, or glucose tolerance test, depending on your random blood glucose test result.
• In someone who has diabetes, an abnormal result on the random blood glucose test may mean that the diabetes is not well controlled. Talk with your provider about your blood glucose goals if you have diabetes.

Other medical problems can also cause a higher-than-normal blood glucose level, including:

• Overactive thyroid gland
• Pancreatic cancer
• Swelling and inflammation of the pancreas (pancreatitis)
• Stress due to trauma, stroke, heart attack, or surgery
• Rare tumors, including pheochromocytoma, acromegaly, Cushing syndrome, or glucagonoma

A lower-than-normal blood glucose level (hypoglycemia) may be due to:

• Hypopituitarism (a pituitary gland disorder)
• Underactive thyroid gland or adrenal gland
• Tumor in the pancreas (insulinoma – very rare)
• Too little food
• Too much insulin or other diabetes medicines
• Liver or kidney disease
• Weight loss after weight loss surgery
• Vigorous exercise

Some medicines can raise or lower your blood glucose level. Before having the test, tell your provider about all the medicines you are taking.

For some people, mainly those who are thin and young, a fasting blood sugar level below 70 mg/dL (3.9 mmol/L) may be normal.

Risks

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

• Excessive bleeding
• Fainting or feeling lightheaded
• Multiple punctures to locate veins
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

References

American Diabetes Association Professional Practice Committee. 2. Classification and diagnosis of diabetes: standards of care in diabetes-2024. Diabetes Care. 2024;47(Suppl 1):S20-S42. PMID: 38078589

US Preventive Services Task Force website. Final recommendation statement: Prediabetes and type 2 diabetes: Screening.

. Released August 24, 2021. Accessed February 20, 2024.

US Preventive Services Task Force website. Final recommendation statement: Prediabetes and type 2 diabetes in children and adolescents: Screening.

. Released September 13, 2022. Accessed February 20, 2024.

Version Info

Last reviewed on: 2/10/2023

Reviewed by: Sandeep K. Dhaliwal, MD, board-certified in Diabetes, Endocrinology, and Metabolism, Springfield, VA. Internal review and update on 02/20/2024 by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.