Fasting and "acute perturbations" are not needed for HbA1c test and it reveals average glycemic control over 3-month period. HbA1c less than 5.6% is considered normal. Glucose status can also be tested through fasting blood sugar (FBS) and requires a blood sample after a patient has fasted for at least eight hours, so it might not be as convenient. Patients who have gotten oral blood samples taken say it feels as if part of a normal procedure, and dentists say it is convenient.In a study that analyzed data from 10,472 adults from 2013 to 2014 and 2015 to 2016, it was revealed that screening for risk of prediabetes in the dental setting has the potential to alert an estimated 22.36 million adults. Diabetes may be asymptomatic for a long time, but since it would be wasteful to test every patient at the dental office, utilizing known risk factors may guide who is ideal for testing. Since a history is already taken at a dental office, a few additional questions would help guide a dentist on narrowing down who the test is recommended for. For example, people with high BMI are at higher risk for diabetes. A study done by the School of Dentistry, Diabetes Research Centre, Mazandaran University of Medical Sciences in Sari, Iran found a relation between periodontitis and the prediabetic condition, and this could be another tool to help guide who might be recommended to take the test.
The fasting glucose may be either normal or mildly elevated.From 10 to 15 percent of adults in the United States have impaired glucose tolerance or impaired fasting glucose. Hemoglobin A1c
Hemoglobin A1c is a measure of the percent of red blood cells that are glycated, or have a glucose molecule attached. This can be used as an indicator of blood glucose level over a longer period of time and is often used to diagnose prediabetes as well as diabetes. HbA1c may not accurately represent blood glucose levels and should not be used in certain medical conditions such as iron-deficiency anemia, Vitamin B12 and folate deficiency, pregnancy, hemolytic anemia, an enlarged spleen, and end-stage kidney failure. Fasting Insulin
Hyperinsulinemia due to insulin resistance may occur in individuals with normal glucose levels and therefore is not diagnosed with usual tests. Hyperinsulinemia precedes prediabetes and diabetes that are characterized by hyperglycemia. Insulin resistance can be diagnosed by measures of plasma insulin, both fasting or during a glucose tolerance test. The use of  fasting insulin to identify patients at risk has been proposed, but is currently not commonly used in clinical practice.The implications of hyperinsulinemia is the risk of comorbidities related to diabetes that may precede changes in blood glucose, including cardiovascular diseases. Screening
Fasting plasma glucose screening should begin at age 30–45 and be repeated at least every three years. Earlier and more frequent screening should be conducted in at-risk individuals.