Diagnosis of Diabetes
Many people are newly diagnosed with diabetes each day in the UK. Although some will have gone to their doctor feeling unwell or with symptoms that have indicated diabetes, for many others the diagnosis comes as a complete surprise. This is because it is quite common for diabetes to be detected during a routine health check or during a period of hospitalization for some other problem. Quite often, initial suspicion of diabetes is raised when sugar is found to be present in a urine sample. However, further testing of blood samples is needed for the diagnosis to be confirmed. It is estimated that 50 per cent of those with the commonest form of diabetes - as many as one million people - are at present undiagnosed and unaware that they have the syndrome. It is probable that many of these people either have no symptoms or that symptoms have developed so slowly and insidiously that they have not recognized that anything is amiss. Ultimately, diagnosis is usually made by testing one or more samples of venous blood (from veins) orplasma. Samples may need to be given on more than one day, depending, to some extent, on whether the person is exhibiting any other symptoms of diabetes. In Britain the diagnostic criteria established by the World Health Organization (WHO) in 1980 and 1985 are still in use, although these have since been challenged and revised by the American Diabetes Association (ADA) through their Expert Committee on the Diagnosis and Classification of Diabetes Mellitus, 1997. These criteria are as follows.
- WHO: A level of glucose at or exceeding 11.1 mmol/1 in
the plasma of venous blood sampled at random. (Or 10.1
mmol/1 if whole venous blood is sampled.) OR A fasting glucose level at or exceeding 7.8 mmol/1 in the plasma of venous blood. (Or 6.7 mmol/1 if whole venous blood is sampled.)
- ADA: A level of glucose at or exceeding 11.1 mmol/1 in
the plasma of venous blood sampled at random, plus
symptoms of diabetes. OR A fasting glucose level at or exceeding 7.0 mmol/1 in the plasma of a venous blood sample. (Fasting is defined as no food or drink containing calories for the previous 8 to 10 hours, usually overnight.)
With both sets of criteria, repeat testing is usually carried out on consecutive days and the diagnosis is confirmed if abnormal readings continue to be obtained. A further test which may be carried out is the Oral Glucose Tolerance Test (OGTT). This has been used for some time and in revised WHO guidelines (1988) continues to be considered very important, especially in cases where the initial results are not clear cut. The OGTT has to be carried out under carefully controlled conditions and requires the person to follow a set of guidelines, summarized below.
- For at least 3 days before the test, the person must eat three meals a day containing plenty of starchy foods such as cereals, bread, pasta, and potatoes.
- An overnight fast, lasting from 10 to 16 hours, is required immediately before the test when only plain water may be drunk.
- The person must refrain from smoking and exercising immediately before and during the test.
- The test must be performed between 8 and 9 a.m. on the morning following the fast.
- A blood sample is taken to obtain a venous plasma glucose level before the test. The person is then given a flavoured drink containing 75 g of glucose dissolved in 250 ml of water, which must be consumed within 5 minutes. A second blood sample is obtained and tested after 120 minutes.
- Urine samples may occasionally require to be tested, every 30 minutes.
The OGTT has been found to be useful in identifying two intermediate states between normality and diabetes,
called Impaired Fasting Glucose (IFG) and Impaired Glucose Tolerance (IGT). In the OGTT, a normal result for venous plasma glucose levels is at or less than 6.0 mmol/1 in the fasting state and less than 7.8 mmol/1 from the second sample taken at 120 minutes. The result for diabetes is at or greater than 7.8 mmol/1 during fasting and greater than 11.1 mmol/1 after 120 minutes.
Blood samples taken at a doctor's surgery, clinic or hospital are normally subjected to laboratory analysis to obtain readings of blood glucose levels. People subsequently diagnosed with diabetes have to continue to monitor their blood glucose levels as part of management of the condition. There is no need to worry that this requires setting up a laboratory in the home! As described later, home testing is quite a simple procedure which does not take up a great deal of time.
More information about diabetes.
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