A fasting blood-sugar level below 100 milligrams per deciliter is considered normal, according to Mayo Clinic. Those with fasting blood-sugar levels between 100 and 125 milligrams per deciliter are said to be pre-diabetic, and those with levels above 125 on two separate occasions are diagnosed with diabetes.
Fasting blood-sugar levels are typically measured in the morning after a person has fasted overnight, states Mayo Clinic. This is just one of several tests that make up a complete diabetes screening procedure. Anyone with a body mass index above 25, and everyone over the age of 45, is advised to undergo diabetes screening tests at least every 3 years.
The oral glucose-tolerance test is similar to the fasting blood-sugar test and also used to screen for diabetes, explains Mayo Clinic. For this test, a patient is asked to fast overnight. He is then asked to drink a sugary liquid while in the doctor's office. The patient's blood sugar levels are measured regularly over the next several hours. After 2 hours, the blood sugar level should be below 140 milligrams per deciliter in a healthy patient. A level above 200 milligrams per deciliter indicates that a patient is diabetic. A doctor may follow up this test with a similar test using a more concentrated solution of glucose if the results are not conclusive.