The worldwide prevalence of diabetes amongst adults in 2011 was estimated at 8.3% which represents approximately 366 million people. This number is expected to rise to 552 million by 20301. The alarming projections are associated with economic development, increasing levels of obesity, lower levels of physical activity, ageing populations and changes in lifestyle patterns globally2. Due to the delay in identifying the condition (>7 years), 20-30% of patients already have complications at diagnosis4. These can include
Much of the cost of diabetes is due to the complications that can arise as a result of the disease. The worldwide cost of diabetes in 2011 was estimated to be $465 billion and this accounts for approximately 11% of total healthcare expenditure1. Early diagnosis and strict management of the patient are essential to minimise personal and economic impacts.
Types of Diabetes
Type 1 Diabetes
Though sometimes called juvenile-onset diabetes or insulin dependent diabetes mellitus (IDDM), type 1 diabetes can affect people of any age and accounts for between 5-10% of all cases3. While the aetiology of this disease is not fully understood, it is known that cellular-mediated autoimmune destruction of the insulin producing β-cells of the pancreas occurs, and people with this form of diabetes need regular injections of insulin to control the levels of glucose in their blood.
Type 2 Diabetes
Sometimes referred to as non-insulin-dependent diabetes or adult-onset diabetes and accounts for between 90-95% of cases, type 2 diabetes is characterised by individuals who are resistant to insulin and usually have relative rather than absolute deficiency. It is thought that there could be many different causes of this form of diabetes but destruction of the β-cells of the pancreas does not occur. The diagnosis of this disease usually occurs after the age of 40 but can occur earlier, especially in populations with high prevalence of diabetes. It is frequently (though not always) associated with obesity.
Gestational Diabetes (GDM)
Gestational diabetes occurs in approximately 1 in 25 pregnancies worldwide when women who have no history of diabetes, develop high blood glucose during pregnancy. It is associated with complications in the period immediately before and after the birth but women with GDM, and their offspring are at an increased risk of developing type 2 diabetes later in life2.
Symptoms of Diabetes
Type 1 diabetes tends to develop suddenly and quickly and symptoms include:
Because type 2 diabetes develops slowly, people may remain unaware of their condition for some time as the classic symptoms may take years to develop or be recognised and many people only being diagnosed when the complications of the illness become evident. There are several risk factors associated with type 2 diabetes which include
Diagnosis and Monitoring of Diabetes
Fasting Plasma Glucose and Oral Glucose Tolerance Test
Diabetes, being characterised by recurrent or persistent hyperglycaemia is diagnosed by measuring blood sugar. The diagnostic cut-off point for diabetes is a fasting plasma glucose (FPG) level greater than 7.0 mmol/L (126mg/dL) or a 2 hour oral glucose tolerance test (OGTT ) level greater than 11.1 mmol/L (200mg/dL). This decision was made on the basis that retinopathy increased linearly above these levels.
In 1997, the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus5 recommended FPG as the more reproducible and easier to perform test but nonetheless a study by Ollerton6 cited by the National Academy of Clinical Biochemistry7 suggests that using a theoretically perfect measurement for glucose, a patient with an average FPG of 126mg/dL could have reported concentrations ranging from 109mg/dL to 143mg/dL in 19 of the 20 days and higher or lower than this on the 20th day. This variation would be more pronounced if the samples were obtained at different times of the day as FPG is higher in the morning than the afternoon8,9.
A third method of assessing glycaemic control of diabetes is the use of glycated serum proteins such as fructosamine to identify plasma glucose concentrations over time. Again, there is no standard reference range available for this test and results can be highly variable from day to day.
Glycated Haemoglobin (HbA1c)
Glycated haemoglobin has a particular clinical interest in diabetes mellitus. Measurement of HbA1c is a clinically useful means of diagnosing diabetes and subsequently assessing glycaemic control in diabetics. Glycated haemoglobin values reflect blood glucose levels over the circulatory half-life of the erythrocyte and correlate significantly with mean blood glucose levels during that time. Therefore, HbA1c measurement of provides a means, independent of multiple measurements such as patient records of self-monitored blood glucose, for assessing the overall efficacy of therapy.
In the past, glycated haemoglobin assays were considered too variable and lacking in standardisation to be considered as a diagnostic assay for diabetes, however due to the Diabetes Control and Complications Trial (DCCT)10, a major clinical study conducted from 1983 to 1993 funded by the National Institute of Diabetes and Digestive and Kidney Diseases(NIDDK), and the National Glycohemoglobin Standardization Program (NGSP), this is no longer the case. The DCCT trial showed that keeping bloody sugar levels as close to normal as possible slows the onset and progression of diseases caused by diabetes, for example:
In 2009, the International Expert Committee reviewed the evidence, existing and emerging, and recommended that HbA1c be used to diagnose diabetes, with 6.5% A1c being the cut-off point. This, like the FPG and OGTT cut-offs, is the inflection point for retinopathy prevalence.11,12