DEFENITION AND CLASSIFICATION OF DIABETES

      Eran Hadar & Moshe Hod

2.1 Definition:

Diabetes mellitus is a group of metabolic disorders characterized by hyperglycaemia due to insufficient pancreatic insulin secretion, impaired tissue response to insulin or a combination of both, with the consequent disturbances in carbohydrate, fat and protein metabolism. The chronic and sustained hyperglycaemia ultimately leads to multi-organ dysfunction. Damage, predominantly involving the small blood vessels, affects mainly the eyes, kidneys, and nervous system; damage to the large blood vessels affects the brain, heart, and legs.

2.2 Classification:

In 1997, the American Diabetes Association (ADA) published new criteria for the classification and diagnosis of diabetes mellitus to replace those in effect since 1979 ⁽¹⁾. The terms insulin-dependent diabetes mellitus (IDDM) and non-insulin dependent diabetes (NIDDM) were eliminated because they often led to misclassifications on the basis of the treatment administered rather than the underlying cause.

 The new ADA classification differentiates four clinical groups of diabetes mellitus:

1.       Type 1 diabetes mellitus ^(2-4) - In type 1 diabetes, which accounts for about 10% of all cases of diabetes, beta cell destruction leads to insulin deficiency and the risk of ketoacidosis. There are three forms.

• Immune-mediated type 1 diabetes - This is the most common form, and can be confirmed by the presence of antibodies against the islet cells (ICA) or their components, such as GAD, IAA, and ICA5/2.
• Idiopathic type 1 diabetes - This type is less well-defined and includes cases in which signs of autoimmune processes are absent.
• Latent autoimmune diabetes in adults (LADA) – this subtype is apparently more prevalent than previously thought, accounting for 5-10% of all cases of diabetes diagnosed in adults.

2.       Type 2 diabetes ^(3-6) - Type 2 diabetes includes most forms of diabetes that derive from combined insulin resistance and imbalance of insulin secretion. Approximately 90% all diabetics have this type. Over recent years, in developed countries, contrary to a decade or so ago, type 2 diabetes has accounted for up to 1/3 of all PreDM). The American College of Obstetricians and Gynecologists (ACOG) has classified GDM and PreGDM into diagnostic subgroups, as shown in Tables 1. PreDM is grouped on the basis of age at onset, duration of disease, and presence of vascular complications – all direct prognostic factors for mother and fetus in the course of pregnancy.

3.       Other specific types ⁽⁴⁾ - About 3% of all cases of diabetes are of other specific types. The many states that fall into this category, albeit relatively rare, include proven genetic defects in beta cell function, genetic defects in insulin activity, exocrine pancreatic diseases, endocrinopathies, diabetes due to medications or chemicals, infections, and the rare autoimmune diabetes and genetic syndromes that involve diabetes. One of the genetic defects in beta cell function is maturity onset diabetes of the young (MODY), which was previously classified under type 2 diabetes mellitus.

4.       Gestational diabetes mellitus ^(4,9-10) - GDM is defined as carbohydrate intolerance of variable severity that is first diagnosed during pregnancy. GDM is grouped on the basis of the fasting blood glucose level, and the mode of treatment, either diet or medical therapy by insulin or oral hypoglycemic agents (Table 2).  A fasting level below 95 mg/dl [5.3 mmol/l], requires only dietary management and is designated A1. A level above 95 mg/dl [5.3 mmol/l] is treated with diet and insulin and is designated A2.

2.3 The Intermediate states:

The Intermediate states ^(1,7-8), are characterized by glucose levels ranging between normal to the lower limit of diabetic values. The intermediate states are risk factors for both diabetes mellitus (1/3 of individuals with IGT will develop diabetes within 10 years) and macrovascular disease (the cardiovascular risk is two- to three times higher). They are usually not associated with the development of microvascular complications unless the blood glucose reaches levels diagnostic of full-blown diabetes (thereby changing the classification). It should be emphasised that although the prognostic significance of IFG is well established, data are still too sparse to determine if it constitutes a risk of macrovascular morbidity equal to that of IGT. The intermediate states are divided into two types:

1.       Impaired fasting glucose (IFG) - This is a relatively new concept that defines individuals with fasting glucose levels between 110 to 125 mg/dl (6.1 - 7.0 mmol/l).

2.       Impaired glucose tolerance (IGT) – This has long been recognized and defines individuals with glucose levels of 140 to 199 mg/dl (7.8 - 11.0 mmol/l) two hours after a 75 g oral glucose load.

Read Also

Table 1: Classification of PreDM
Group	Age at onset (yr)		Duration of disease (yr)	Vascular complication	Treatment
B	Over 20		Less than 10	None	Diet-insulin
C	Less than 10   and/or  10-19			None	Diet-insulin
D	Less than 10    and/or over 20			Retinopathy-Background type	Diet-insulin
F	All ages	Any duration		Nephropathy	Diet-insulin
R	All ages	Any duration		Retinopathy-Proliferative	Diet-insulin
H	All ages	Any duration		Cardiac disease	Diet-insulin
T	All ages	Any duration		After organ transplant	Diet-insulin

Table 2: Classification of GDM
Group	Fasting Glucose	2-hr Postprandial Glucose	Treatment
A1	<95 mg/dl (<5.3 mmol/l)	<120 mg/dl (<6.7 mmol/l)	Diet only
A2	>95 mg/dl    and/or          >120 mg/dl >5.3 mmol/l  and/or          >6.7 mmol/l		Diet + Insulin / Oral Hypoglycemics