Often, prediabetes has no signs or symptoms. But it's important to watch for the classic red flags of type 2 diabetes, including:

• Increased thirst
• Frequent urination
• Extreme hunger
• Unexplained weight loss
• Fatigue
• Blurred vision
• Slow-healing sores or frequent infections

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To understand prediabetes, first you must understand how sugar (glucose) is normally processed in the body.

Glucose is a main source of energy for the cells that make up your muscles and other tissues. Glucose comes from two major sources: the food you eat and your liver. During digestion, sugar is absorbed into the bloodstream. Normally, sugar then enters cells with the help of insulin.

The hormone insulin comes from the pancreas, a gland located just behind the stomach. When you eat, your pancreas secretes insulin into your bloodstream. As insulin circulates, it acts like a key by unlocking microscopic doors that allow sugar to enter your cells. Insulin lowers the amount of sugar in your bloodstream. As your blood sugar level drops, so does the secretion of insulin from your pancreas.

Your liver acts as a glucose storage and manufacturing center. When your insulin levels are low — when you haven't eaten in a while, for example — your liver releases the stored glucose to keep your glucose level within a normal range.

When you have prediabetes, this process begins to work improperly. Instead of moving into your cells, sugar builds up in your bloodstream. This occurs when your pancreas doesn't make enough insulin or your cells become resistant to the action of insulin or both. Exactly why this happens is uncertain, although excess fat — especially abdominal fat — and inactivity seem to be important factors.

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The same factors that increase the risk of developing type 2 diabetes increase the risk of developing prediabetes, including:

• Weight. Being overweight is a primary risk factor for prediabetes. The more fatty tissue you have — especially around your abdomen — the more resistant your cells become to insulin.
• Inactivity. The less active you are, the greater your risk of prediabetes. Physical activity helps you control your weight, uses up glucose as energy and makes your cells more sensitive to insulin.
• Age. The risk of prediabetes increases as you get older, especially after age 45. Often, that's because people tend to exercise less, lose muscle mass and gain weight as they age. But diabetes is also increasing dramatically among children, adolescents and younger adults.
• Family history. The risk of prediabetes increases if a parent or sibling has type 2 diabetes.
• Race. Although it's unclear why, people of certain races — including blacks, Hispanics, American Indians and Asian-Americans — are more likely to develop prediabetes.
• Gestational diabetes. If you developed gestational diabetes when you were pregnant, your risk of later developing diabetes increases. If you gave birth to a baby who weighed more than 9 pounds, you're also at increased risk of diabetes.
• Polycystic ovary syndrome. For women, having polycystic ovary syndrome — a common condition characterized by irregular menstrual periods, excess hair growth and obesity — increases the risk of diabetes.

Other conditions associated with diabetes include:

• High blood pressure
• High levels of low-density (LDL), or "bad," cholesterol
• Low levels of high-density lipoprotein (HDL), or "good," cholesterol
• High levels of triglycerides, another fat in the blood

When these conditions — high blood pressure, high blood sugar and abnormal blood fats — occur together along with obesity, they are associated with resistance to insulin. This is often referred to as metabolic syndrome.

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Consult your doctor if you're concerned about diabetes or if you notice any type 2 diabetes symptoms — increased thirst and frequent urination, extreme hunger, weight loss, fatigue, blurred vision, and slow-healing sores or frequent infections.

Ask your doctor about blood glucose screening if you have any risk factors for prediabetes. For example:

• You're overweight.
• You're inactive.
• You're age 45 or older.
• You have a family history of type 2 diabetes.
• You're black, Hispanic, American Indian or Asian-American.
• You developed gestational diabetes when you were pregnant or gave birth to a baby who weighed more than 9 pounds.
• You have polycystic ovary syndrome.
• You have high blood pressure.
• You have high LDL cholesterol, low HDL cholesterol or high triglycerides.

In fact, the American Diabetes Association recommends routine blood glucose screening for everyone beginning at age 45.

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The American College of Endocrinology suggests prediabetes testing for anyone who has a family history of type 2 diabetes and for those who are obese or have metabolic syndrome. Women with a personal history of gestational diabetes also should be tested.

In June 2009, an international committee composed of experts from the American Diabetes Association, the European Association for the Study of Diabetes and the International Diabetes Federation recommended that prediabetes testing include the:

• Glycated hemoglobin (A1C) test. This blood test indicates your average blood sugar level for the past two to three months. It works by measuring the percentage of blood sugar attached to hemoglobin, the oxygen-carrying protein in red blood cells. The higher your blood sugar levels, the more hemoglobin you'll have with sugar attached. An A1C level between 6 and 6.5 percent is considered prediabetes. A level of 6.5 percent or higher on two separate tests indicates you have diabetes.

If the A1C test isn't available, or if you have certain conditions that can make the A1C test inaccurate — such as if you're pregnant or have an uncommon form of hemoglobin (known as a hemoglobin variant) — your doctor may use the following tests to diagnose diabetes:

• Fasting blood sugar test. A blood sample will be taken after you fast for at least eight hours or overnight. With this test, a blood sugar level lower than 100 milligrams per deciliter (mg/dL) is normal. A blood sugar level from 100 to 125 mg/dL is considered prediabetes. This is sometimes referred to as impaired fasting glucose (IFG). A blood sugar level of 126 mg/dL or higher may indicate diabetes.
• Oral glucose tolerance test. A blood sample will be taken after you fast for at least eight hours or overnight. Then you'll drink a sugary solution, and your blood sugar level will be measured again after two hours. A blood sugar level less than 140 mg/dL is normal. A blood sugar level from 140 to 199 mg/dL is considered prediabetes. This is sometimes referred to as impaired glucose tolerance (IGT). A blood sugar level of 200 mg/dL or higher may indicate diabetes.

If your blood sugar level is normal, your doctor may recommend a screening test every three years. If you have prediabetes, further testing may be needed. Your doctor may recommend a glucose tolerance test once a year. This test can identify individuals who have diabetes sooner than the fasting blood glucose test can. Your doctor may also recommend an annual microalbuminuria test, which checks for protein in your urine — an early sign of damage to the kidneys. Twice a year, your doctor should check your fasting blood sugar and A1C levels. Your blood fats — total cholesterol, HDL cholesterol, LDL cholesterol and triglycerides — also need to be checked twice a year.

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If you have prediabetes, 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. Guidelines from the American College of Endocrinology suggest the following to treat prediabetes:

• Eat healthy foods. Choose foods low in fat and calories and high in fiber. Focus on fruits, vegetables and whole grains. Strive for variety to help you achieve your goals without compromising taste or nutrition.
• Get more physical activity. Aim for 30 to 60 minutes of moderate physical activity at least five days a week. Take a brisk daily walk. Ride your bike. Swim laps. If you can't fit in a long workout, break it up into smaller sessions spread throughout the day.
• Lose excess pounds. If you're overweight, losing just 5 percent to 10 percent of your body weight — only 10 to 20 pounds, if you weigh 200 pounds — can reduce the risk of developing type 2 diabetes. To keep your weight in a healthy range, focus on permanent changes to your eating and exercise habits. Motivate yourself by remembering the benefits of losing weight, such as a healthier heart, more energy and improved self-esteem.

• Take medications as needed. Sometimes medications — such as the oral diabetes drugs metformin (Glucophage) and acarbose (Precose) — also are an option if you're at high risk of diabetes. This includes if your prediabetes is worsening or you have cardiovascular disease, fatty liver disease or polycystic ovary syndrome.

  In other cases, medications to control cholesterol — statins, in particular — and high blood pressure medications are needed. Your doctor might prescribe low-dose aspirin therapy to help prevent heart and blood vessel disease. Healthy lifestyle choices remain essential, however.

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

• Eat healthy foods.
• Get more physical activity.
• Lose excess pounds.

If the list looks familiar, you're onto something. The same lifestyle changes that can treat or even reverse prediabetes help prevent the condition, too.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

Many alternative therapies — including beta glucans, bitter melon, cassia cinnamon, ginseng, gymnema and stevia — have been touted as possible ways to treat or prevent type 2 diabetes. However, there's no conclusive evidence that any of these alternative therapies are effective.

If you're considering dietary supplements or other alternative therapies to treat or prevent prediabetes, consult your doctor. He or she can help you weigh the pros and cons of specific alternative therapies.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.