Prediabetes (Borderline Diabetes)

Medically Reviewed by Michael Dansinger, MD on December 08, 2021
4 min read


Prediabetes is when your blood sugar level is higher than it should be but not high enough for your doctor to diagnose diabetes. They might call it impaired fasting glucose or impaired glucose tolerance.

People with type 2 diabetes almost always had prediabetes first. But it doesn’t usually cause symptoms. About 84 million people over age 20 in the U.S. have prediabetes, but 90% don’t know that they have it.

Prediabetes treatment can prevent more serious health problems, including type 2 diabetes and problems with your heart, blood vessels, eyes, and kidneys.

If you have symptoms, you might notice that:

  • You're a lot thirstier than usual.
  • You pee a lot.
  • Your vision is blurry.
  • You’re a lot more tired than usual.

You’re more likely to get prediabetes if you:

Get tested for prediabetes if those things apply to you and if you:

  • Have had an unusual blood sugar reading
  • Have heart disease
  • Show signs of insulin resistance, which means your body makes insulin but doesn't respond to it the way it should. These include darkened areas of skin, trouble concentrating, and more fatigue or hunger than usual.

Your doctor will do at least one of these tests:

Fasting plasma glucose test. You won’t eat for 8 hours, and then a technician will take your blood to test the sugar levels. The results are:

  • Normal if your blood sugar is less than 100 milligrams per deciliter (mg/dL)
  • Prediabetes if your blood sugar is 100 to 125 mg/dL
  • Diabetes if your blood sugar is 126 mg/dL or higher

Oral glucose tolerance test. First, you'll have a fasting plasma glucose test. Then, you'll drink something sugary. Two hours after that, a technician will take and test more blood. The results are:

  • Normal if your blood sugar is less than 140 mg/dL after the second test
  • Prediabetes if your blood sugar is 140 to 199 mg/dL after the second test
  • Diabetes if your blood sugar is 200 mg/dL or higher after the second test

Hemoglobin A1c test. This blood test shows your average blood sugar levels for the past 2 to 3 months. Doctors give it to people who have diabetes to see if their blood sugar levels are under control. They can also use it to diagnose prediabetes or diabetes. The results are:

  • Normal if it’s 5.6% or less
  • Prediabetes if it’s 5.7 to 6.4%
  • Diabetes if it’s 6.5% or above

You may need to take the test again to confirm the results.

Doctors diagnose prediabetes based on the same blood sugar levels, no matter the person’s age. The American Diabetes Association says children 10 and older should be tested if they’re overweight or obese and have:

  • A family member with type 2 diabetes
  • A mother who had gestational diabetes while pregnant with the child
  • Native American, Black, Hispanic, Asian American, or Pacific Islander heritage
  • Signs of insulin resistance or conditions linked to it, such as a low birth weight, high blood pressure, or polycystic ovary syndrome

If a child who has a high chance of getting prediabetes has normal test results, the American Diabetes Association advises testing them again at least every 3 years. 

Without treatment, prediabetes can become type 2 diabetes or cause other serious problems including:

  • Kidney disease
  • Blindness
  • High blood pressure
  • Nerve problems (peripheral neuropathy)
  • Loss of a limb (amputation)

Take these steps to treat prediabetes:

  • Eat a healthy diet and lose weight. Losing 5% to 10% of your weight can make a huge difference.
  • ExercisePick something you enjoy, like walking. Try to get at least 30 minutes a day, 5 days a week. You can start with less time and work your way up to a half-hour if you need to. Check with your doctor before you do more than that.
  • Stop smoking.
  • Get your blood pressure and cholesterol under control.
  • Take medication like metformin (Glucophage) to lower your blood sugar if you’re at high risk of diabetes.

There’s no official diet, but four swaps can reverse prediabetes and lower your chances of getting type 2 diabetes:

  • Choose whole grains and whole-grain products over processed carbs like white bread, potatoes, and breakfast cereals.
  • Drink coffeewater, and tea instead of sugary drinks.
  • Choose good fats like those in vegetable oil, nuts, and seeds over those in margarine, baked goods, and fried foods.
  • Trade red meat and processed meats for nuts, whole grains, poultry, and fish.

Exercising and eating foods low in carbohydrates, sugars, fats, and salt can also help prevent prediabetes. Other tips include:

  • Don’t smoke.
  • Don’t have more than one alcoholic drink a day.
  • Take blood sugar medications as your doctor prescribes.