Diagnosis of Type 2 Diabetes Mellitus

Diagnosis of Type 2 Diabetes Mellitus

There is a continuum of risk for poor patient outcomes as glucose tolerance progresses from normal to overt type 2 diabetes. AACE-defined glucose tolerance categories are listed in Table 1.1

Table 1. AACE Diagnostic Criteria for Glucose Abnormalities1




FPG, mg/dL
(measured after 8-hour fast)




Impaired fasting glucose



PPG, mg/dL
(measured with an OGTT performed 2 hours after 75 g oral glucose load taken after 8-hour fast)




Impaired glucose tolerance



Hemoglobin A1C, %
(screening only)




High risk/prediabetes



Abbreviations: FPG, fasting plasma glucose; OGTT, oral glucose tolerance test; PPG, postprandial glucose.

  • A random glucose value ≥200 mg/dL with symptoms of hyperglycemia (polyurea, polydipsia, or polyphagia) also indicates diabetes.
  • In the absence of unequivocal hyperglycemia or severe metabolic stress, either FPG or PPG should be tested again on a different day to confirm the diagnosis.

A1C should be used to screen for—but not to diagnose—glucose abnormalities. Any value of ≥5.5% calls for further testing with an FPG test or OGTT.

The diagnostic cut points recommended by the American Diabetes Association (ADA) differ slightly from the AACE recommendations; please see the ADA Standards of Medical Care in Diabetes for details.2

In addition to glucose criteria, type 1 diabetes mellitus (T1DM) is diagnosed according to the presence of autoantibodies to glutamic acid decarboxylase, pancreatic islet (beta) cells, or insulin.1,2

Type 2 diabetes mellitus (T2DM) accounts for 90% of diabetes cases and is usually identified in individuals 30 years or older who are overweight or obese and/or have a family history of diabetes.1,2

Gestational diabetes mellitus (GDM) is diagnosed based on OGTT results in pregnant women without previously diagnosed diabetes.1,2

Use of A1C in Diagnosis of Diabetes

While the ADA advocates using A1C as a diagnostic measure,2 AACE recommends using A1C primarily for screening because it can be misleading or inaccurate in some populations such as African Americans and the elderly, as well as in the following hemoglobinopathies:1,3

  • Iron deficiency
  • Hemolytic anemia
  • Thalassemias
  • Spherocytosis
  • Severe hepatic disease
  • Severe renal disease

A1C represents an average of blood glucose over the lifetime of an erythrocyte, which is approximately 2-3 months.4 However, differences in erythrocyte turnover, cell membrane permeability to glucose, and hemoglobin glycation and deglycation, among other processes, may all lead to an altered relationship between A1C and mean glycemia in any given individual.3,5,6

Diagnosing T2DM in Pediatric Patients

The incidence of T2DM in the young is rising, although it remains uncommon relative to other forms of diabetes, particularly in children. In preadolescent children where the distinctions between types of diabetes may be unclear, further testing for T1DM can be performed by assessing immune markers. Immune marker assessment can help distinguish between T1DM and T2DM in children and adolescents where there is often phenotypic overlap between these disorders. Consideration can also be given to monogenic forms of diabetes (formerly known as maturity onset diabetes of the young [MODY]) by careful evaluation of family history. Genetic testing is currently available for MODY2 and MODY3. Monogenic forms of diabetes are rare. Because inheritance of these disorders is usually due to autosomal dominant mutations that regulate insulin secretion, there is usually a history of early onset nonketotic diabetes in at least one family member that may help in identifying others with the condition.1

In 2009, the International Society of Pediatric and Adolescent Diabetes published an extensive Clinical Practice Consensus Guidelines for the care of diabetes in children, which is available on its Web site.7


  1. Handelsman Y, Mechanick JI, Blonde L, et al. American Association of Clinical Endocrinologists Medical Guidelines for Clinical Practice for developing a diabetes mellitus comprehensive care plan. Endocr Pract. 2011;17(suppl 2):1-53.
  2. American Diabetes Association. Standards of medical care in diabetes—2013. Diabetes Care. 2013;36(suppl 1):S11-66.
  3. American Association of Clinical Endocrinologists/American College of Endocrinology statement on the use of hemoglobin A1C for the diagnosis of diabetes. Endocr Pract. 2010;16:155-156.
  4. Gallagher EJ, Le Roith D, Bloomgarden Z. Review of hemoglobin A(1c) in the management of diabetes. J Diabetes. 2009;1:9-17.
  5. Bloomgarden ZT, Einhorn D. Hemoglobin A1C in diabetes diagnosis: time for caution. Endocr Pract. 2010;16:5-6.
  6. Bloomgarden ZT. A1C: recommendations, debates, and questions. Diabetes Care. 2009;32:e141-147.
  7. Hanas R, Donaghue KC, Klingensmith G, Swift PG. ISPAD clinical practice consensus guidelines 2009 compendium. Pediatr Diabetes. 2009;10(suppl 12):1-210.