Classification and Diagnosis of Diabetes

Historically, diabetes has been broken down into two main categories: type 1 diabetes, previously called juvenile diabetes, and type 2 diabetes, previously called adult onset diabetes. Much has been learned about the underlying nature of diabetes in recent years and the classification and diagnosis of diabetes has changed to reflect this new knowledge. Doctors no longer refer to just two types of diabetes, and though most people with diabetes have either type 1 or type 2, diabetes comes in many forms. The two main types of diabetes -- type 1 and type 2 -- are fundamentally different conditions that can require very different treatments to achieve the common goal of keeping blood glucose levels as close to normal as possible.

On June 23, 1997, during its 57th Annual Scientific Sessions, James R. Gavin, III, MD, PhD, of the Howard Hughes Medical Institute and chair of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus announced a new set of Classification Guidelines and Diagnosis Guidelines. The Expert Committee hopes these guidelines will

  1. Focus on the cause of diabetes rather than the treatment regimen
  2. Develop a standard that can be used worldwide
  3. Eliminate the confusion surrounding the use of insulin

In addition, declaring fasting blood sugar levels above 126 mg/dl (7.0 mmol/l) to be diabetes reflects data that indicates that the risk of microvascular complications from high blood sugar levels increases significantly around 126 mg/dl. The Committee hopes that the new diagnostic guidelines will bring up to two million Americans with diabetes into the health care system for treatment before they develop complications.

Note that the new classification guidelines use Arabic numbers (1 and 2) rather than Roman numerals (I and II), and that the terms insulin-dependent diabetes and noninsulin-dependent diabetes are no longer used.

Classification of Diabetes
Type 1 Characterized by beta cell destruction, usually leading to absolute insulin deficiency.

Type 1 diabetes accounts for 5-10% of people with diabetes. It has two forms:

  1. Immune-Mediated Diabetes Mellitus:
    Results from a cellular mediated autoimmune destruction of the beta cells of the pancreas. One or more key antibodies are found in 85-90% of people with this form of type 1 diabetes. People with this form of type 1 diabetes always require insulin to survive. This is the most common form of type 1 diabetes and is sometimes refered to as "Type 1A diabetes."

  2. Idiopathic Diabetes Mellitus:
    Refers to forms of the disease that have no known etiologies. These forms are much less common than immune-mediated type 1 and are mostly found in people with African or Asian ancestry. People with this form of type 1 diabetes often lack antibodies found in immune-mediated type 1 diabetes, and may be able to go without insulin therapy for some periods of time. This form of type 1 diabetes is sometimes refered to as "Type 1B diabetes."
Type 2

Diseases of insulin resistance that usually have relative (rather than absolute) insulin deficiency.

Can range from predominant insulin resistance with relative insulin deficiency to predominant insulin deficiency with some insulin resistance. Many people have type 2 diabetes for years before being diagnosed. Most people with type 2 diabetes are obese. Treatment usually includes advice to lose weight and increase exercise, as well as oral medications.


A metabolic stage intermediate between normal glucose homeostasis and diabetes. A risk factor for diabetes and cardiovascular disease.

  1. Impaired Fasting Glucose
    Fasting plasma glucose higher than normal, and less than diagnostic.

  2. Impaired Glucose Tolerance
    Plasma glucose higher than normal, and less than diagnostic, following administration of a glucose load of 75 grams.

Glucose intolerance in pregnancy.

Gestational diabetes is any glucose intolerance that is first noticed during pregnancy, regardless of the treatment. Some women with gestational diabetes require only changes to their diet, while some women require insulin injections. The American Diabetes Association estimates that 4% of pregnancies in the United States are complicated by gestational diabetes.


Diabetes caused by other identifiable etiologies.

  1. Genetic defects of beta cell function (e.g., MODY 1, 2, 3)
  2. Genetic defects in insulin action
  3. Diseases of the exocrine pancreas (e.g., cancer of the pancreas, cystic fibrosis, pancreatitis)
  4. Endocrinopathies (e.g., Cushing's)
  5. Drug or chemical induced (e.g., steroids)
  6. Infection (e.g., rubella, Coxsackie, CMV)
  7. Uncommon forms of immune-related diabetes
  8. Other genetic syndromes

Diagnosing Diabetes
Stage Test
(mmol/L -- mg/dl)
Fasting Plasma Glucose Test (FPG)
(Preferred) 1
Casual Plasma Glucose Test Oral Glucose Tolerance Test (OGTT)
75 gram load
Diabetes Fasting Plasma Glucose (FPG) greater than or equal to
7.0 / 126 2
Casual Plasma Glucose greater than or equal to
11.1 / 200 plus symptoms 3
Two-hour plasma glucose (2hPG) greater than or equal to
11.1 / 200 4
Fasting Plasma Glucose (FPG) greater than or equal to
7.0 / 126 2
n/a Two-hour plasma glucose (2hPG) greater than or equal to
8.6 / 155 
Impaired Fasting Glucose (IFG) = FPG greater than or equal to
5.6 / 100
and less than
7.0 / 126
n/a Impaired Glucose Tolerance (IGT) = 2hPG greater than or equal to
7.8 / 140
and less than
11.1 / 200
Normal Fasting Plasma Glucose (FPG) less than
5.6 / 100
n/a Two-hour plasma glucose (2hPG) less than
7.8 / 140


  1. The FPG is the preferred test for diagnosis, although any of the three is acceptable. In the absence of unequivocal hyperglycemia with acute metabolic decompensation, one of these three tests should be used on a different day to confirm the diagnosis.
  2. Fasting is defined as no caloric intake for at least eight hours.
  3. Casual is defined as any time of day without regard to time since last meal; symptoms are the classic ones of polyuria, polydipsia, and unexplained weight loss.
  4. OGTT should be performed using a 75 gram glucose load. The OGTT is not recommended for routine clinical use.

For More Information


  1. Report of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus
  2. Diabetes Diagnosis From the National Diabetes Information Clearinghouse
  3. Follow-up Report on the Diagnosis of Diabetes Mellitus from the November 2003 issue of Diabetes Care. Free full text available in PDF format.

Last updated October 9, 2004

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Last Updated: Sat Oct 09 07:47:58 2004
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