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Do I Have Prediabetes or Diabetes? Guide to the A1C, FPG, and OGTT Tests, Plus Tips for Prevention

Prediabetes vs. diabetes

If you’ve been diagnosed with prediabetes, you may wonder what that means. It’s a condition where your blood glucose levels are above normal, but not high enough for you to be diagnosed with diabetes. Many doctors consider prediabetes to be the first stage of type 2 diabetes.

Studies show that 15 to 30 percent of people with prediabetes will develop diabetes in as little as five years without intervention, such as weight loss or increased physical activity. In fact, most people who get type 2 diabetes had prediabetes first.

Prediabetes is serious in and of itself. People with this condition have a greater risk of developing cardiovascular disease than those without it.

How is prediabetes diagnosed?

There are three tests that doctors can do in order to determine whether you have high blood sugar.


This blood test, which is also called hemoglobin A1c, HbA1c, or glycosylated hemoglobin, measures the percentage of sugar that is attached to your hemoglobin. Hemoglobin is a protein in your red blood cells. The higher the A1C, the higher your average blood sugar levels have been running over the past two or three months.

A normal A1C is below 5.7 percent. An A1C between 5.7 percent and 6.4 percent suggests prediabetes. An A1C of 6.5 or more indicates type 2 diabetes if the test is confirmed. If your results are questionable, your doctor will retest your A1C on another day to confirm the diagnosis.

Normal A1C resultsbelow 5.7%
Prediabetes A1C results5.7 to 6.4%
Diabetes A1C resultsabove 6.4%

Fasting plasma glucose

The fasting plasma glucose (FPG) test is a blood test that’s done after you’ve been fasting overnight. It measures the sugar in your blood. A normal fasting glucose test is lower than 100 milligrams per deciliter (mg/dL). A result between 100 and 125 mg/dL is diagnostic for prediabetes. One that is 126 mg/dL or above is indicative of diabetes. It’s recommended to retest this another day to confirm the diagnosis.

Normal FPG resultsbelow 100 mg/dL
Prediabetes FPG results100 to 125 mg/dL
Diabetes FPG resultsabove 125 mg/dL

Random plasma glucose

A random blood glucose (RPG) test is a blood test that is done any time of day that you aren’t fasting. It measures the sugar level in your blood at that moment in time. An RPG result that’s over 200 mg/dL is indicative of diabetes, especially if you are having symptoms of diabetes such as excessive thirst, hunger, or urination. If your level is higher, your doctor will use one of the other tests listed to confirm the diagnosis.

Oral glucose tolerance test

The oral glucose tolerance test (OGTT) takes a little more time than the other two glucose tests for diabetes. In this test, your blood is taken after an overnight fast, and then again two hours after you drink a sugary drink. It’s normal for blood sugar to rise after the drink. Normal blood sugar falls to below 140 mg/dL within two hours, however. If your blood sugar is between 140 and 199 mg/dL, your doctor will diagnose prediabetes. Anything 200 mg/dL or above is diagnostic for type 2 diabetes.

Normal OGTT resultsbelow 140 mg/dL
Prediabetes OGTT results140 to 199 mg/dL
Diabetes OGTT resultsabove 199 mg/dL

Managing prediabetes

If you’ve been diagnosed with prediabetes, there are steps you can take to help reduce your risk for developing diabetes and return your blood glucose to a normal range.

Eat a healthy diet

Maintaining a healthy, balanced diet can help reduce your risk for diabetes. Changing your diet can be challenging, so start by making small changes. Track everything you’re eating for a few days so you can understand what food groups you may be over- or undereating. You should be eating foods every day from each of the six food groups:

  • vegetables
  • fruits
  • grains
  • protein
  • dairy
  • fats

Using the information from your food log, you can begin to make small changes. The goal is to choose less processed, whole foods, instead of highly processed foods that contain added sugar, little fiber, and unhealthy fats.

For example, if you aren’t eating the recommended servings of vegetables, try adding one serving of vegetables a day to your diet. You can do this by having a salad with lunch or dinner, or snacking on carrot sticks. Just be careful about add-ons like salad dressing or dips. They can sneak in unhealthy fats or extra calories.

You’ll also want to work on reducing the number of empty-calorie foods and beverages you’re consuming, as well as switching out simple carbohydrate foods for complex carbohydrates. Examples of substitutions you can try to include:

Get active

Exercise is also important for managing your blood glucose. Aim for 30 minutes of exercise five days a week.

As with dietary changes, you should also start slow and work your way up. If you aren’t very active, you can start by parking further away from a building’s entrance or taking a flight of stairs instead of an escalator or elevator. Taking a walk around the block with your family or a neighbor after dinner is another great way to add in some exercise.

Once you get more comfortable with increasing your activity level, you can start doing more vigorous activities, like jogging or attending a workout class.

Remember to always get your doctor’s approval before beginning a new workout routine. They can let you know if there are activities you should avoid or things you should monitor, like your heart rate.

Maintain a healthy weight

Eating a balanced diet and exercising can help you lose or maintain weight. Ask your doctor what a healthy weight is for you. Work with them to determine how many calories you should be eating. If you need to lose weight, ask them how much weight you should be losing per week to stay healthy. Crash diets and extreme workout plans may make for entertaining television, but they aren’t realistic for long-term maintenance, and often they’re unhealthy as well.


Prediabetes often leads to diabetes, and most of the time there are no noticeable symptoms. That’s why it’s important to have your blood glucose levels tested, especially if you’re over age 45 or have a family history of diabetes. If you’re overweight, testing before age 45 is recommended if one of these other risk factors is present:

  • physical inactivity
  • a family history of diabetes
  • race (African-Americans, Native Americans, Asian-Americans, and Pacific Islanders being at higher risk)
  • for women, birth of a baby weighing over 9 pounds
  • blood pressure over 140/90 mm Hg
  • HDL (good) cholesterol levels under 35 mg/dL or triglyceride levels over 250 mg/dL
  • an A1C equal to or greater than 5.7 percent or a high fasting blood sugar over 100 mg/dL on a previous test
  • other conditions associated with insulin resistance, such as polycystic ovarian syndrome or acanthosis nigricans
  • history of cardiovascular disease

If you do have prediabetes, you can reduce your risk for type 2 diabetes by exercising about 30 minutes each day and losing just five to 10 percent of your body weight. Your doctor may also start you on a medication to help control your blood sugar.

Prediabetes doesn’t have to progress to type 2 diabetes. Lifestyle changes can help you get and keep your blood sugar levels within their normal range.

Content licensed from:

Written by: Linda Hepler, RN
Medically reviewed on: Jan 10, 2017: Peggy Pletcher, MS, RD, LD, CDE

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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