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. Glucose Testing and Interpretation1


High Risk for Diabetes


FPG < 100 mg/dL

FPG ≥100-125 mg/dL

FPG ≥126 mg/dL

2-hour PG <140 mg/dL (measured with an OGTT performed 2 hours after 75 g oral glucose load taken after 8-hour fast)

2-hour PG ≥140-199 mg/dL

2-hour PG ≥200 mg/dL
Random PG ≥200 mg/dL plus symptoms of diabetes (polyurea, polydipsia, or polyphagia)

A1C < 5.5%

5.5% to 6.4%
For screening of prediabetesa


Abbreviations: A1C = hemoglobin A1C; FPG = fasting plasma glucose; IFG = impaired fasting glucose; IGT = impaired glucose tolerance; PG = plasma glucose.

a A1C should be used only for screening prediabetes. The diagnosis of prediabetes, which may manifest as either IFG or IGT, should be confirmed with glucose testing.

b Glucose criteria are preferred for the diagnosis of DM. In all cases, the diagnosis should be confirmed on a separate day by repeating glucose or A1C testing. When A1C is used for diagnosis, follow-up glucose testing should be done when possible to help manage diabetes.

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 (T1D) is diagnosed according to the presence of autoantibodies to glutamic acid decarboxylase, pancreatic islet (beta) cells, or insulin.1,2

Type 2 diabetes (T2D) 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 diabetes1,2

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 T2D in Pediatric Patients

The incidence of T2D 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 T1D can be performed by assessing immune markers. Immune marker assessment can help distinguish between T1D and T2D 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, Bloomgarden ZT, Grunberger G, et al. American Association of Clinical Endocrinologists and American College of Endocrinology Clinical practice guidelines for developing a diabetes mellitus comprehensive care plan—2015. Endocr Pract. 2015;21(suppl 1):1-87.
  2. American Diabetes Association. 2. Classification and diagnosis of diabetes. Diabetes Care. 2017;40:S11-S24.
  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. Sperling MA, ed. ISPAD Clinical Practice Consensus Guidelines 2014. Available at: http://www.ispad.org/?page=ISPADClinicalPract