Blood sugar levels before meals typically range from 70 to 80 milligrams per deciliter, according to WebMD. Two hours after eating, they are less than 140 milligrams per deciliter.
Consistently high blood sugar levels are often a sign of diabetes, says WebMD. Doctors use various tests to determine whether an individual has diabetes. The fasting plasma glucose test can indicate the disease if the blood sugar level is higher than 126 milligrams per deciliter after eight hours of fasting. The oral glucose tolerance test, in which the patient consumes a sugary drink after eight hours of fasting, indicates diabetes if the blood sugar level exceeds 200 milligrams per deciliter.
It is possible to prevent the onset of diabetes through diet and exercise, WebMD notes.