Tayside Diabetes MCN Handbook
Classification of Diabetes

The terms IDDM and NIDDM should be avoided as they classify patients on the basis of diabetes treatment rather than the pathogenesis of the disease.


Type 1 Diabetes (previously IDDM)

This results from an absolute deficiency of insulin due to pancreatic beta-cell destruction. It more commonly presents acutely before the age of 35, but can occur at any age. Patients are insulin dependent and prone to ketoacidosis.


Type 2 Diabetes (previously NIDDM)

This results from a relative deficiency of or insensitivity to insulin and is more commonly diagnosed over the age of 35, although can occur in younger (especially obese) individuals. Although the onset of Type 2 diabetes is less dramatic than that of Type 1 diabetes, the long term sequelae are similar and equally devastating, as both Type 1 and Type 2 patients are at risk of developing the microvascular and macrovascular complications of the disease.

For this reason, Type 2 diabetes should never be referred to as 'mild diabetes'.


LADA (Latent Autoimmune Diabetes of Adulthood)

LADA is a term used to describe patients who have an insidious onset of diabetes similar to type 2 diabetes, but who have presence of pancreatic autoantibodies (GAD antibodies) suggestive of an autoimmune aetiology. Patients with LADA progress onto insulin quicker than patients with type 2 diabetes, although in the UKDPS only 50% progressed to insulin within 6 years.


Monogenic Diabetes

Approximately 5% of diabetes is thought to be caused by single gene mutations that can be passed through the family. These should be suspected in anyone with a strong family history of diabetes particularly if their diabetes appears atypical. The two most common forms of monogenic diabetes are Maturity Onset Diabetes of the Young (MODY) and Maternally Inherited Diabetes and Deafness (MIDD). Classically a MODY family will have 2-3 generations with non-insulin requiring diabetes with at least one member being diagnosed before the age of 25 years. One subtype is associated with renal cysts and dysfunction. MIDD is caused by a mitochondrial 3243 mutation, so is passed from mother to child. It is characterized by deafness and young onset diabetes and should be suspected in anyone presenting with diabetes and familial deafness.


Cystic fibrosis related diabetes (CFRD)

Because of the increased survival of patients with cystic fibrosis, there is an increasing prevalence of CFRD, with an average age of diagnosis age 18 to 24. The diabetes is multifactorial in origin, but is primarily due to insulin deficiency with systemic illness also increasing insulin resistance. In the early stages, the fasting glucose is normal but patients have high post prandial blood glucose driven by the high carbohydrate loads that patients with CF require. Hence children and young adults with CF should be screened for CFRD by monitoring post-prandial blood glucose or more formally with oral glucose tolerance testing. Patients with CFRD are usually treated with insulin (initially an rapid acting insulin analogue with meals), although there is some evidence to suggest sulphonylureas may be effective. Insulin treatment has been shown to improve BMI and lung function in patients with CFRD.


Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) is defined as carbohydrate intolerance of variable severity with onset or first recognition during pregnancy. It does not exclude that the glucose intolerance may have antedated pregnancy, therefore a post-natal OGTT should be performed. Women with a history of GDM have a 60% chance of developing diabetes (usually Type 2) within the subsequent 20 years and this risk is increased by obesity. For this reason they should be advised to control their weight and have an annual fasting glucose measurement performed. For further details see Diabetes and Women

Women with a history of GDM should be screened for the condition in future pregnancies and have a fasting glucose checked annually.


Pre-Diabetes States:


Impaired Glucose Tolerance (IGT)

IGT is a state of impaired glucose regulation, diagnosed on glucose tolerance testing, which confers an increased risk of future diabetes of 2-5% per year. Patients with IGT tend to have higher blood pressure and plasma triglycerides when compared to non-diabetic individuals.


Impaired Fasting Glycaemia (IFG)

The term IFG has been introduced to classify individuals with fasting glucose values above the normal range but below those diagnostic of diabetes i.e. FPG > 6.0 mmol/L but < 7.0mmol/L. Diabetes UK recommends that all such individuals should have an oral glucose tolerance test to exclude a diagnosis of diabetes.

IGT and IFG are risk categories for future diabetes and/or cardiovascular disease. Patients with either condition should have fasting plasma glucose checked annually (or sooner if symptoms occur) and receive advice on the avoidance of obesity and the benefits of regular exercise. Co-existing cardiovascular risk factors should be treated aggressively.


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