Skip to main content

Is the Hemoglobin A1c Test Used to Diagnose Diabetes?

Reasons for using a hemoglobin A1c test have included it being a faster and easier diagnostic test, and there is no need for fasting beforehand.

Since the American Diabetes Association (ADA) released its 2014 Clinical Practice Recommendations, the hemoglobin A1c has been used to diagnose diabetes. The use of A1c testing had not been previously recommended for diagnostic purposes, in part due to lack of standardization of the assay. However, methods of A1c testing based on the reference assay used in the Diabetes Control and Complications Trial and certified by the National Glycohemoglobin Standardization Program have supported its use. Reasons for using an A1c test have included it being a faster and easier diagnostic test, and there is no need for fasting beforehand.

Since an A1c test indirectly measures average blood glucose over a period of time, there are certain conditions which may limit its use in diagnosing diabetes. For example, during pregnancy and with some anemias, the turnover of red blood cells is affected, so other diagnostic tests would be recommended in these instances. Evidence has also suggested that A1c levels may vary depending on age, race and ethnicity. In the case of Medicare coverage for medical nutrition therapy (MNT), as well as for diabetes self-management training, there is a requirement of a diabetes diagnosis using methods other than A1c as this benefit was developed prior to the 2014 ADA recommendations (For more information, consult The Guide to Medicare Preventive Services and the Diabetes Self-Management Education/Training and Medical Nutrition Therapy Services Order Form.)

For the purpose of confirming a diabetes diagnosis, it may require a repeat of the same test or the use of an alternate one and on two different occasions. According to the ADA's Standards of Medical Care in Diabetes – 2020, the following diagnostic tests and criteria may be used to diagnose diabetes:

  • A1C: greater than or equal to 6.5%.
  • Fasting Plasma Glucose (FPG): greater than or equal to 126 mg/dl (no energy intake for at least 8 hours prior).
  • Oral Glucose Tolerance Test (also called the OGTT): a 2-hour plasma glucose greater than or equal to 200 mg/dL during OGTT involving administration of 75 g glucose (using 75 g anhydrous glucose dissolved in water).
  • Random (also called Casual) Plasma Glucose Test: greater than or equal to 200 mg/dL and classic symptoms of hyperglycemia (e.g., polyuria, polydipsia, and unexplained weight loss).

While the test used in diagnosing diabetes can vary depending on the patient, it is recommended that an A1c test be performed at regular intervals to monitor glycemic control. The frequency will be based on whether treatment goals are being met and as treatment recommendations are modified.

Diabetes self-management education and support (DSMES), also referred to as diabetes self-management training (DSMT), is advocated following a diabetes diagnosis, as well as annually, and in the event treatment goals are not attained or complications develop. DSMES, along with a referral for MNT (conducted as a separate service), are critical to an individual's successful management of diabetes.

According to a recent Consensus Paper developed jointly by several organizations, including the ADA and the Academy, "DSMES results in an average A1C reduction of 0.45-0.57% when compared with usual care for people with type 2 diabetes treated with a variety of modalities…". In addition, a referral for MNT provided by a registered dietitian nutritionist (RDN) has shown to be cost-effective and resulted in favorable clinical outcomes and improved quality of life for individuals with diabetes.

Optimal diabetes management requires a systematic approach and involvement of the patient/client, along with a coordinated team of dedicated health care professionals. RDN's play an instrumental role in providing personalized nutrition interventions, which can help individuals with diabetes achieve glycemic control and reduce the risk of diabetes-related complications.


Join the Academy

Members of the Academy of Nutrition and Dietetics receive exciting benefits including complimentary continuing professional education opportunities, discounts on events and products in, invitations to exclusive members-only events and more!