People with prediabetes have glucose levels that are higher than normal but not high enough yet to indicate diabetes. The condition used to be called borderline diabetes. Most people with prediabetes may not have the symptoms, but they are considered to be at high risk of developing heart disease.

Normally, your body produces a hormone called insulin to help your cells use the energy (glucose) found in food. With diabetes, either your body doesn't make enough insulin or doesn't efficiently use the insulin it does produce. When glucose builds up in the blood, it can damage the tiny blood vessels in the kidneys, heart, eyes, and nervous system.

With prediabetes, the subtle balance between glucose and insulin has been thrown off. The pancreas may not be able to produce enough insulin after a meal to "clear" the incoming glucose from the blood. Or cells may be insulin resistant. When cells are insulin resistant, they won't allow the insulin to escort glucose from the bloodstream into them. Too much glucose in the blood is also called high blood sugar or hyperglycemia. A low blood sugar level is called hypoglycemia.

If you have prediabetes, you're at high risk of developing type 2 diabetes as well as the serious medical problems associated with diabetes, including heart disease  and stroke. With prediabetes, you are at a 50% higher risk of heart disease and stroke than someone who does not have prediabetes.