- Diagnosis and Classification of Diabetes
- Initial Assessment and Criteria for Specialist Referral
- Glycaemic Control in Type 2 Diabetes - Oral Hypoglycaemic Agents
- Indications for Insulin in Type 2 Diabetes
- Hypertension
- Dyslipidaemia
- Aspirin Therapy in Diabetes
- Retinopathy
- Nephropathy
- Neuropathy and Foot Ulcers
- Sexual Dysfunction in Men
- Diabetes in Pregnancy and Pre-conception Guidance
1. Diagnosis and Classification of Diabetes
The term diabetes mellitus describes several syndromes of abnormal carbohydrate metabolism that are characterised by hyperglycaemia. It is associated with a relative or absolute impairment in insulin secretion, along with varying degrees of peripheral resistance to the action of insulin.
Classification – In the new classification, there is no distinction between primary and secondary causes of diabetes. The terms type 1 and type 2 are to be used, whereas terms like insulin-dependent, non-insulin-dependent, juvenile-onset, maturity-onset, adult-onset, maturity-onset diabetes of the young (MODY) are to be eliminated. This change reflects an attempt to classify diabetes according to aetiologic differences (as far as they are understood) and to move away from descriptions based upon age at onset or type of treatment. The majority of patients with type 1 diabetes have autoimmune destruction of the pancreatic beta cells as the underlying cause, an absolute requirement for insulin therapy, and will develop diabetic ketoacidosis (DKA) if not given insulin. However, some patients with type 1 diabetes will not meet all of these criteria and some patients with type 2 diabetes can develop DKA under certain circumstances (severe infection or other illness) and many require treatment with insulin.
In the US, Canada, and Europe, over 80% of cases of diabetes are due to type 2 diabetes, 5-10% to type 1 diabetes, and the remainder to other specific causes.
Definition Of Diabetes Mellitus – The diagnosis of diabetes mellitus is easy to establish when a patient presents with classic symptoms of hyperglycaemia (thirst, polyuria, weight loss, visual blurring), and has a fasting blood glucose concentration at or above 7.0mmol/L or a random value at or above 11.1mmol/L. Never base the diagnosis of diabetes solely on a stick reading of a finger prick glucose – it must be confirmed on a venous plasma measurement in a laboratory. Fasting glucose estimations require a certainty of no calorie intake for 10-16 hours. Once diabetes confirmed, test urine for ketones. Type 1 diabetes is likely if significant ketonuria (ie +++), short history, marked weight loss, low BMI and relatively young (<40 years).
In the old classification, both the National Diabetes Data Group (NDDG) in the US and World Health Organisation (WHO) established diagnostic criteria for normal glucose tolerance and diabetes based upon an oral glucose tolerance test (OGTT). They had also suggested that a category between normality and diabetes should be used called impaired glucose tolerance (IGT), because subjects with IGT are at increased risk of developing overt diabetes and atherosclerotic vascular disease, even if they do not develop diabetes.
New criteria – The new diagnostic criteria strongly suggest that the diagnosis of diabetes be made on the basis of fasting blood glucose only. The OGTT should not be used for epidemiological research, because it is an imprecise test with poor reproducibility. A provisional report from the WHO agrees with the new definitions, but suggests continued use of the OGTT for patients with blood glucose values in the "uncertain range".
The following definitions have been suggested:
Normal – Fasting plasma glucose (FPG) <6.1mmol/L.
Impaired fasting glucose (IFG) – Fasting plasma glucose between 6.1-6.9 mmol/L. This is broadly equivalent to the category of IGT, which was based upon both fasting and two-hour values in the OGTT.
Diabetes mellitus – FPG at or above 7.0mmol/L or a random (or two-hour value in an OGTT) at or above 11.1mmol/L.
The proportion of people in the latter two categories increases with age and, at all ages, the proportion with IFG/IGT or type 2 diabetes increases with obesity. As an example, it has been estimated that about 11% of Americans aged 20-74 years have IGT and 6% have type 2 diabetes.
The shift from using two hour values on an OGTT to FPG causes changes in the prevalence of diabetes mellitus, depending on the population studied and almost twice as many subjects may be classified as diabetic by the new than the old fasting criteria.
Haemoglobin A1c – There remain serious problems in the standardisation of HbA1c assays and, at the present time, the diagnosis of diabetes mellitus should not be made on the basis of HbA1c values.
Classification – The following aetiological classification has been proposed:
Type 1 diabetes – Type 1 diabetes is characterised by destruction of the pancreatic beta cells, leading to absolute insulin deficiency. As noted above, this is usually due to autoimmune destruction of the pancreatic beta cells (type 1A), but some patients have no evidence of autoimmunity and have no other known cause for beta-cell destruction. They are said to have idiopathic type 1B diabetes mellitus.
Type 2 diabetes – Type 2 diabetes is by far the most common type of diabetes, and is characterised by variable degrees of insulin deficiency and resistance.
Genetic defects of beta-cell function – Approximately 2 to 4 percent of patients with type 2 diabetes present at a young age, have mild disease, and autosomal dominant transmission. This condition was formerly called maturity-onset diabetes of the young (MODY). These patients are quite heterogeneous and clinical characteristics are not reliable in predicting the underlying pathogenesis. Several genetic abnormalities have been found that account for the disorder in many of these patients. Some members of the same family may have the genetic defect but do not develop diabetes; the reason for this is unclear.
Genetic defects in insulin action – There are a series of rare abnormalities in the insulin receptor (due to a genetic defect or the polycystic ovary syndrome) or in the structure of insulin itself.
Diseases of the exocrine pancreas – Any disease that damages the pancreas, or removal of pancreatic tissue, can result in diabetes. There is a wide variability in the frequency with which this occurs, primarily determined by the degree of pancreatic insufficiency. Among patients with pancreatic exocrine disease, diabetes is more likely to occur in those with a family history of type 1 or type 2 diabetes. Examples include cystic fibrosis, hereditary haemochromatosis and fibrocalculous pancreatic diabetes, which is a unique form of diabetes secondary to tropical non-alcoholic pancreatitis that is endemic in certain parts of the world (eg, southern India).
Endocrinopathies – Several hormones, such as adrenaline, glucagon, cortisol, and growth hormone, antagonise the action of insulin. Increased release of these hormones constitutes the protective counter-regulatory response to hypoglycaemia. On the other hand, primary over secretion of these hormones can result in IFG or overt diabetes eg Cushing's syndrome, acromegaly, phaeochromocytoma and glucagonoma. Although thyroxine is not a counter-regulatory hormone, hyperthyroidism can also disrupt glucose metabolism.