Prediabetes doesn't usually have any signs or symptoms.

One possible sign of prediabetes is darkened skin on certain parts of the body. Affected areas can include the neck, armpits and groin.

Classic signs and symptoms that suggest you've moved from prediabetes to type 2 diabetes include:

• Increased thirst
• Frequent urination
• Increased hunger
• Fatigue
• Blurred vision
• Numbness or tingling in the feet or hands
• Frequent infections
• Slow-healing sores
• Unintended weight loss

When to see a doctor

See your health care provider if you're concerned about diabetes or if you notice any type 2 diabetes signs or symptoms. Ask your health care provider about blood sugar screening if you have any risk factors for diabetes.

The exact cause of prediabetes is unknown. But family history and genetics appear to play an important role. What is clear is that people with prediabetes don't process sugar (glucose) properly anymore.

Most of the glucose in your body comes from the food you eat. When food is digested, sugar enters your bloodstream. Insulin allows sugar to enter your cells — and lowers the amount of sugar in your blood.

Insulin is produced by a gland located behind the stomach called the pancreas. Your pancreas sends insulin to your blood when you eat. When your blood sugar level starts to drop, the pancreas slows down the secretion of insulin into the blood.

When you have prediabetes, this process doesn't work as well. As a result, instead of fueling your cells, sugar builds up in your bloodstream. This can happen because:

• Your pancreas may not make enough insulin
• Your cells become resistant to insulin and don't allow as much sugar in

The same factors that increase the odds of getting type 2 diabetes also increase the risk of prediabetes. These factors include:

• Weight. Being overweight is a primary risk factor for prediabetes. The more fatty tissue you have — especially inside and between the muscle and skin around your abdomen — the more resistant your cells become to insulin.
• Waist size. A large waist size can indicate insulin resistance. The risk of insulin resistance goes up for men with waists larger than 40 inches and for women with waists larger than 35 inches.
• Diet. Eating red meat and processed meat, and drinking sugar-sweetened beverages, is associated with a higher risk of prediabetes.
• Inactivity. The less active you are, the greater your risk of prediabetes.
• Age. Although diabetes can develop at any age, the risk of prediabetes increases after age 35.
• Family history. Your risk of prediabetes increases if you have a parent or sibling with type 2 diabetes.
• Race or ethnicity. Although it's unclear why, certain people — including Black, Hispanic, American Indian and Asian American people — are more likely to develop prediabetes.
• Gestational diabetes. If you had diabetes while pregnant (gestational diabetes), you and your child are at higher risk of developing prediabetes.
• Polycystic ovary syndrome. Women with this common condition — characterized by irregular menstrual periods, excess hair growth and obesity — have a higher risk of prediabetes.
• Sleep. People with obstructive sleep apnea — a condition that disrupts sleep repeatedly — have an increased risk of insulin resistance. People who are overweight or obese have a higher risk of developing obstructive sleep apnea.
• Tobacco smoke. Smoking may increase insulin resistance and can increase the risk of type 2 diabetes in people with prediabetes. Smoking also increases your risk of complications from diabetes.

Other conditions associated with an increased risk of prediabetes include:

• High blood pressure
• Low levels of high-density lipoprotein (HDL) cholesterol, the "good" cholesterol
• High levels of triglycerides — a type of fat in your blood

Metabolic syndrome

When certain conditions occur with obesity, they are associated with insulin resistance, and can increase your risk for diabetes — and heart disease and stroke. A combination of three or more of these conditions is often called metabolic syndrome:

• High blood pressure
• Low levels of HDL
• High triglycerides
• High blood sugar levels
• Large waist size

Prediabetes has been linked with long-term damage, including to your heart, blood vessels and kidneys, even if you haven't progressed to type 2 diabetes. Prediabetes is also linked to unrecognized (silent) heart attacks.

Prediabetes can progress to type 2 diabetes, which can lead to:

• High blood pressure
• High cholesterol
• Heart disease
• Stroke
• Kidney disease
• Nerve damage
• Fatty liver disease
• Eye damage, including loss of vision
• Amputations

Healthy lifestyle choices can help you prevent prediabetes and its progression to type 2 diabetes — even if diabetes runs in your family. These include:

• Eating healthy foods
• Getting active
• Losing excess weight
• Controlling your blood pressure and cholesterol
• Not smoking

The American Diabetes Association (ADA) recommends that diabetes screening for most adults begin at age 35. The ADA advises diabetes screening before age 35 if you're overweight and have additional risk factors for prediabetes or type 2 diabetes.

If you've had gestational diabetes, your health care provider will likely check your blood sugar levels at least once every three years.

There are several blood tests for prediabetes.

Glycated hemoglobin (A1C) test

This test indicates your average blood sugar level for the past 2 to 3 months.

In general:

• Below 5.7% is normal
• Between 5.7% and 6.4% is diagnosed as prediabetes
• 6.5% or higher on two separate tests indicates diabetes

Certain conditions can make the A1C test inaccurate — such as if you're pregnant or have an uncommon form of hemoglobin.

Fasting blood sugar test

A blood sample is taken after you haven't eaten for at least eight hours or overnight (fast).

Blood sugar values are expressed in milligrams of sugar per deciliter (mg/dL) or millimoles of sugar per liter (mmol/L) of blood. In general:

• Less than 100 mg/dL (5.6 mmol/L) is normal
• 100 to 125 mg/dL (5.6 to 6.9 mmol/L) is diagnosed as prediabetes
• 126 mg/dL (7.0 mmol/L) or higher on two separate tests is diagnosed as diabetes

Oral glucose tolerance test

This test is less commonly used than the others, except during pregnancy. You'll need to fast overnight and then drink a sugary liquid at the primary care provider's office or lab testing site. Blood sugar levels are tested periodically for the next two hours.

In general:

• Less than 140 mg/dL (7.8 mmol/L) is normal
• 140 to 199 mg/dL (7.8 to 11.0 mmol/L) is consistent with prediabetes
• 200 mg/dL (11.1 mmol/L) or higher after two hours suggests diabetes

If you have prediabetes, your health care provider will typically check your blood sugar levels at least once a year.

Children and prediabetes testing

Type 2 diabetes is becoming more common in children and adolescents, likely due to the rise in childhood obesity.

The ADA recommends prediabetes testing for children who are overweight or obese and who have one or more other risk factors for type 2 diabetes, such as:

• Family history of type 2 diabetes
• Being of a race or ethnicity associated with an increased risk
• Low birth weight
• Being born to a mother who had gestational diabetes

The ranges of blood sugar level considered normal, prediabetes and diabetes are the same for children and adults.

Children who have prediabetes should be tested annually for type 2 diabetes — or more often if the child experiences a change in weight or develops signs or symptoms of diabetes, such as increased thirst, increased urination, fatigue or blurred vision.

Healthy lifestyle choices can help you bring your blood sugar level back to normal, or at least keep it from rising toward the levels seen in type 2 diabetes.

To prevent prediabetes from progressing to type 2 diabetes, try to:

• Eat healthy foods. A diet high in fruits, vegetables, nuts, whole grains and olive oil is associated with a lower risk of prediabetes. Choose foods low in fat and calories and high in fiber. Eat a variety of foods to help you achieve your goals without compromising taste or nutrition.
• Be more active. Physical activity helps you control your weight, uses up sugar for energy and helps the body use insulin more effectively. Aim for at least 150 minutes of moderate or 75 minutes of vigorous aerobic activity a week, or a combination of moderate and vigorous exercise.
• Lose excess weight. If you're overweight, losing just 5% to 7% of your body weight — about 14 pounds (6.4 kilograms) if you weigh 200 pounds (91 kilograms) — can significantly reduce the risk of type 2 diabetes. To keep your weight in a healthy range, focus on permanent changes to your eating and exercise habits.
• Stop smoking. Stopping smoking can improve the way insulin works, improving your blood sugar level.
• Take medications as needed. If you're at high risk of diabetes, your health care provider might recommend metformin (Glumetza). Medications to control cholesterol and high blood pressure might also be prescribed.

Children and prediabetes treatment

Children with prediabetes should follow the lifestyle changes recommended for adults with type 2 diabetes, including:

• Losing weight
• Eating fewer refined carbohydrates and fats, and more fiber
• Reducing portion sizes
• Eating out less often
• Spending at least one hour every day in physical activity

Medication generally isn't recommended for children with prediabetes unless lifestyle changes aren't improving blood sugar levels. If medication is needed, metformin is usually the recommended drug.

Many alternative therapies have been touted as possible ways to treat or prevent type 2 diabetes. But there's no definitive evidence that any alternative treatments are effective. Therapies that have been said to be helpful in type 2 diabetes and are also likely to be safe, include:

• Cassia cinnamon
• Flaxseed
• Ginseng
• Magnesium
• Oats
• Soy
• Xanthan gum

Talk to your health care provider if you're considering dietary supplements or other alternative therapies to treat or prevent prediabetes. Some supplements or alternative therapies might be harmful if combined with certain prescription medications. Your health care provider can help you weigh the pros and cons of specific alternative therapies.

You're likely to start by seeing your primary care provider. He or she may refer you to a specialist in diabetes treatment (endocrinologist), a dietitian or a certified diabetes educator.

Here's some information to help you get ready for your appointment.

What you can do

Before your appointment, take these steps:

• Ask about any pre-appointment restrictions. You may need to fast for at least eight hours before your appointment so that your health care provider can measure your fasting blood sugar level.
• List symptoms you've been having and for how long.
• List all medications, vitamins and supplements you take, including the doses.
• List key personal and medical information, including other conditions, recent life changes and stressors.
• Prepare questions to ask your health care provider.

Some basic questions to ask include:

• How can I prevent prediabetes from turning into type 2 diabetes?
• Do I need to take medication? If so, what side effects can I expect?
• I have other health conditions. How can I best manage them together?
• How much do I need to exercise each week?
• Should I avoid any foods? Can I still eat sugar?
• Do I need to see a dietitian?
• Can you recommend any local programs for preventing diabetes?

What to expect from your doctor

Your health care provider is likely to ask you a number of questions, such as:

• Has your weight changed recently?
• Do you exercise regularly? If so, for how long and how often?
• Do you have a family history of diabetes?