Chances are you know someone with type 2 diabetes. It's the most common form of diabetes—millions of Americans have it. But have you heard of something called prediabetes?

It's a condition that also affects millions of Americans—and one that everyone should learn about.

Here are three things you need to know about prediabetes to help protect your health:

1. It isn't the same as diabetes—yet. Prediabetes is a serious warning that type 2 diabetes is on its way. If you're told you have prediabetes, it means your blood sugar (glucose) level is higher than normal, but not quite high enough to be type 2 diabetes. But if your glucose level continues to go up—and you don't take steps to bring it down—you'll probably develop full-blown diabetes.

2.You could have it but not know it. You can't count on having symptoms of prediabetes to warn you of the condition, because often there are none. The only way to know for sure is to have your blood sugar level measured.

Your doctor may recommend that you be tested for the condition if you're 45 or older. Even if you're younger than 45, your doctor might also want you to get tested if you are overweight and have other risk factors, such as you have a family history of diabetes; are African American, Asian American or Hispanic/Latino; have high blood pressure; or are not physically active.

3.Small steps can go a long way toward reversing it. And now the really good news: Prediabetes can often be turned around with lifestyle changes. Losing some weight (shedding even 7 percent of your body weight can help), exercising regularly, and eating less fat and calories can help prevent or delay type 2 diabetes.

Sources: American Diabetes Association; National Institute of Diabetes and Digestive and Kidney Diseases