If you have lots of symptoms of diabetes then a random test taken at any time of the day may suffice. However, it is usual to request a fasting blood test taken after 8 hours of fasting. The glucose result will either fall within a normal range or be abnormally high.
The exact figures for a variety of different abnormal glucose categories vary slightly from country to country depending on which diagnostic criteria are followed. If you travel you may get confused but generally there are two main ways to express the results. These are in mmol/l as in the UK or in mg/dl as in the USA. The conversion factor is 18 and this can easily be done on your mobile phone. For example, 10 mmol/l multiplied by 18 is 180 mg/dl.
A normal fasting glucose is 6 mmol/l or below. If it is a bit higher (6.1 to 6.9 mmol/l) it is referred to as impaired fasting glucose or pre-diabetes. A level of blood glucose equal to or greater than 7 mmol/l confirms the diagnosis of diabetes.
In the USA and in many other countries where the figures are expressed as mg/dl, the cut off point above which a diagnosis of diabetes is made is 126 mg/dl.
The blood glucose levels may fall into a grey area where the diagnosis may be in doubt. The reason for taking this situation seriously is because even mildly raised glucose values increase the silent build up of plaque within the coronary arteries. A clear health focus worldwide is to reduce the burden of premature coronary artery disease and so even this category of glucose impairment is considered an important target to diagnose and treat. A glucose tolerance test is often requested in order to help with this exercise.
During the glucose tolerance test (OGTT), the patient attends a laboratory for a fasting glucose level before proceeding to drink a specified amount of sugary solution. This is often 75g of glucose although there are other variations of this test. The subsequent blood tests done over 2 hours should show a normal rise in blood glucose followed by a fall to normal levels as your body produces insulin in order to deal with the sudden energy intake.
An abnormal OGGT after 2 hours is confirmed if the blood glucose stays high. If it is above 11.1 mmol/l (200 mg/dl) then a diagnosis of diabetes is confirmed. If the level is 7.8 -11 mmol/l (140-199 mg/dl) the condition is referred to as impaired glucose intolerance.
The World Health Organisation (WHO) has recently added another diagnostic test for diabetes diagnosis. This is the long- term Haemoglobin A1c (HbA1c) which measures accumulated glucose in the body over about 3 months. Although this test has traditionally been used in clinics to judge complication risk in patients with established diabetes, it is now also a useful aid as a diagnostic test. An HbA1c level of 48 mmol/mol (6.5%) and above is now recommended as the cut off point for diagnosing diabetes.
The diagnosis also revolves around an analysis of symptoms and clinical history. This is because there should also be an assessment of the type of diabetes in the knowledge that this will influence the choice of treatment. For example a diagnosis of Type 1 diabetes will almost certainly mean insulin injections from the outset. Type 2 diabetes patients can usually be treated with oral medication, at least initially.
Some people with diabetes secondary to other conditions such as pancreatitis or the taking of steroids will inevitably require special considerations with respect to their general medical management as well as their specific diabetes treatment.
Diabetes is associated with many complications including diabetic eye disease, kidney failure, foot ulcers and coronary heart disease even with only mildly raised blood glucose levels. For this reason any diagnosis of diabetes, however mild it may appear, is taken seriously.
The first step is to review the blood glucose results with your doctor and establish a clear pathway of treatment and general management. There is every chance that with optimal treatment your general health will improve, your life expectancy will remain normal and that the horror stories you read about in magazines, newspapers or on the Internet will remain only distant possibilities.