What are normal adult blood sugar levels?

In a nondiabetic adult, a normal fasting blood sugar level can range from 70 to 100 milligrams per deciliter, and a normal result for a random blood sugar test is lower than 125 milligrams per deciliter, states MedlinePlus. Blood glucose levels vary according to factors, such as the time of day when a blood glucose test is performed.

When a blood glucose test is performed within 2 hours after eating, a normal reading is less than 140 milligrams per deciliter, notes WebMD. Fasting blood glucose test results that are in the range of 100 to 125 milligrams per deciliter is referred to as prediabetes. A reading that is 126 or over indicates that a patient may have diabetes, according to MedlinePlus.