Prediabetes: a warning sign and a possible turning point

Prediabetes is a term that has become more popular recently, partly to help raise awareness surrounding diabetes. Prediabetes is what it sounds like: something that comes before diabetes. When you have prediabetes, your blood sugars are elevated, but they are not quite elevated enough for you to be diagnosed with full-blown diabetes. It is a warning sign that diabetes may be in your future. But if you take the right steps, you can use your diagnosis of prediabetes as motivation to make the lifestyle modifications necessary to prevent developing full-blown diabetes.

(It should be remembered that prediabetes is only a precursor to type 2 diabetes mellitus (T2DM), not to the other forms of diabetes.)

• Type 1 diabetes mellitus is an autoimmune disease that is not preceded by prediabetes.

• Gestational diabetes refers to diabetes that is brought on by pregnancy.

• Diabetes insipidus is an unrelated disease that has to do with a hormone called ADH, not with insulin.

Prediabetes is sometimes referred to as "impaired fasting glucose" or "impaired glucose tolerance." These terms come from the fact that with prediabetes, your body has a hard time regulating blood sugar, which is also called blood glucose.

The best way to define prediabetes may be to explain what is going on in diabetes (remember, we are only referring to T2DM here).

T2DM is a disease in which the body does not respond to insulin well. Insulin is a hormone in the body that is secreted by the pancreas in response to elevated blood sugar levels. When you eat food, your blood sugar levels rise. In response to this rise, insulin is released into the bloodstream. Insulin then binds to receptors on fat, muscle, and liver cells, allowing those cells to take up glucose and either use it for energy or store it for later use. When your body doesn't respond to insulin as well, this is called insulin resistance.

Several things can cause insulin resistance. However, the most significant risk factors are genetics, being overweight, having abdominal fat, and living a sedentary lifestyle. While many people believe that insulin resistance and T2DM are directly caused by obesity, not all people who are obese develop insulin resistance and T2DM. Similarly, not all people with insulin resistance and T2DM are obese.

At first, to compensate for insulin resistance, your pancreas goes into overdrive. It pumps out extra insulin (which can be detected in the blood and is called hyperinsulinemia) and does its best to keep blood sugar levels in the normal range. However, after time, your pancreas has a hard time keeping up. This is either because your tissues respond to insulin even less or because your pancreas gets burnt out and stops making enough insulin. Either way, your body becomes less effective at regulating glucose, and blood sugar rises as a result.

When blood sugar levels become uncontrolled, you are diagnosed with diabetes. Several tests can be used to diagnose diabetes, and each has a specific cutoff level (see below).

Prediabetes occurs when you are on your way to diabetes. Screening tests reveal elevated blood glucose levels but not high enough to warrant a diabetes diagnosis. However, just because you don't have diabetes does not mean that prediabetes is harmless. Having prediabetes means you are at risk of developing diabetes. But it also puts you at risk for cardiovascular and microvascular disease (heart disease and blood vessel disease).

A staggering number of people have prediabetes. According to the Centers for Disease Control and Prevention (CDC), 1 in 3 Americans have prediabetes, and 90% of them don't even know (CDC, 2019).

The risk factors for prediabetes are essentially the same as the risk factors for T2DM. These are generally broken down into the things you can change and the things you cannot change. Things you can change include:

• Being overweight

• Having a large waist size

• Eating an unhealthy diet 

• Decreased physical activity

• Smoking

Things you cannot change include:

• Age >45, race (non-Hispanic whites have the lowest risk), 

• Family history of T2DM

• A personal history of certain medical conditions, including:

  • Acanthosis nigricans (darkening of the armpits and neck)

  • Gestational diabetes (diabetes brought on by pregnancy) 

  • Hypertension (high blood pressure)

  • Polycystic ovary syndrome (also called PCOS) 

  • Sleep apnea (difficulty breathing while sleeping)

For lots of people, prediabetes has no symptoms. This is part of the reason many people may have prediabetes without even knowing it. However, some may experience similar symptoms as those seen in T2DM. These include:

• Increased thirst (polydipsia)

• Frequent urination (polyuria)

• Lack of energy (fatigue)

Three of the same tests that are done to screen for T2DM can be performed to detect prediabetes. Diagnosis can then be made based on these tests. To confirm the diagnosis of T2DM, these tests need to be done more than once on separate days.

The Fasting Plasma Glucose (FPG) Test

This is a blood test that is performed after you have been fasting (not eating or drinking) for at least eight hours. Results can be interpreted as:

• FPG 70-99 mg/dL is considered normal

• FPG 100-125 mg/dL indicates you may have prediabetes

• FPG >125 mg/dL indicates you may have diabetes

The Oral Glucose Tolerance Test (OGTT)

This is a blood test that is performed after you have been fasting for at least eight hours and then are given a measured dose (typically 75g in the United States) of a glucose solution to drink. Your blood is then drawn two hours later. Results can be interpreted as:

• 2-hour blood sugar level <140 mg/dL is considered normal

• 2-hour blood sugar level 140-199 mg/dL indicates you may have prediabetes

• 2-hour blood sugar level >199 mg/dL indicates you may have diabetes

The Hemoglobin A1C test (HbA1c)

This is a blood test that gives a reasonable estimate of blood sugar levels over the prior two to three months. It does not require fasting. Results can be interpreted as:

• HbA1c <5.7 is considered normal

• HbA1c 5.7-6.4 indicates you may have prediabetes

• HbA1c >6.4 means you may have diabetes

How do you prevent prediabetes from becoming type 2 diabetes? Is it possible to reverse prediabetes?

Prediabetes is a warning sign that T2DM may be in your future, but that does not necessarily have to be the case. T2DM is a debilitating, lifelong disease that is a risk factor for many other problems later in life. As such, it is essential to use your diagnosis of prediabetes as a "wake up call" to do everything you can to prevent its progression into T2DM. Moreover, prediabetes is recognized as a reversible disorder, which means that, with treatment, you can return your blood glucose levels into the normal range.

If you have prediabetes, it’s recommended that you get screened every 1-2 years to see if you have developed diabetes. According to the American Diabetes Association (ADA), research indicates that certain lifestyle modifications can reduce your risk of developing T2DM by 58%. The ADA recommends weight-loss equaling 7% of your body weight and engaging in moderate exercise for at least thirty minutes a day at least five days a week (ADA, n.d.).

Additional lifestyle changes include eating a healthier diet that is rich in whole, unprocessed foods and quitting smoking. A study looking at 3,234 people with prediabetes found that lifestyle interventions can improve risk factors for cardiovascular disease, including high blood pressure and certain components of cholesterol (Diabetes, 2005).

Lastly, your healthcare provider may prescribe you medication for your prediabetes. Metformin (brand name Glucophage) is a medication that has long been used to treat T2DM. Now, some providers are using it for prediabetes as well, although this is an off-label use (meaning the FDA has not explicitly approved metformin for prediabetes). Metformin works by decreasing the amount of sugar released into the bloodstream by the liver and by making the body more sensitive to insulin. Metformin is not as effective at preventing progression to T2DM as lifestyle modifications, but one study did find that it reduced the progression to T2DM by 31% (Knowler, 2002). It is more effective at reducing the risk in younger, obese patients as well as in women with a history of gestational diabetes (UpToDate, 2019). It is less effective in older or less overweight patients. People taking metformin for prediabetes should undergo at least annual screening for T2DM.

To learn more about what you can do to prevent T2DM, check out the National Diabetes Prevention Program (DPP).

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

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Current version

August 22, 2019

Written by

Mike Bohl, MD, MPH, ALM

Fact checked by

Tzvi Doron, DO

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About the medical reviewer

Tzvi Doron, DO

Dr. Tzvi Doron is Board Certified in Family Medicine by the American Board of Family Medicine.