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PRACTICE: Tim A Holt and Claire J Holt Raised blood glucose concentration BMJ 2008; 337: a1073 [Full text]

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Raised blood glucose and use of the glucose tolerance test

Charles van Heyningen   (16 October 2008)

Raised blood glucose and use of the glucose tolerance test 16 October 2008
Charles van Heyningen, chemical pathologist Aintree Hospitals, Liverpool, L9 7AL Send response to journal: Re: Raised blood glucose and use of the glucose tolerance test	Diabetes UK recommends that, with no symptoms, diagnosis of diabetes should not be based on a single glucose determination but requires confirmatory plasma venous determination. At least one additional glucose test result on another day with a value in the diabetic range is essential, either fasting, from a random sample or from the two hour post glucose load. If the fasting or random values are not diagnostic the two hour value should be used. Diabetes UK also recommends that the diagnosis is confirmed by a glucose measurement performed in an accredited laboratory on a venous plasma sample, although the WHO do give values for whole blood as well. This should mean that there is less need to perform oral glucose tolerance testing on the majority of the population, although in the elderly and some ethnic minority groups the fasting glucose may not be a reliable indicator of diabetes. For this group, and in the absence of symptoms of diabetes, Diabetes UK would recommend the use of an oral glucose tolerance test (OGTT) as the definitive second test. The patient presented in the consultation scenario has unequivocal fasting hyperglycaemia, if the sample is fasting, without obvious symptoms and is not elderly, although ethnicity is not described. In these circumstances a repeat fasting glucose is much simpler and more convenient for the patient and is usually enough to confirm the diagnosis of diabetes. An audit in our region has shown that the OGTT is often performed poorly in primary care with a wide variation in glucose loads (65 to 85 grams of glucose) given as Lucozade. If the second fasting plasma glucose does not confirm diabetes the OGTT by a standardised protocol should be the definitive third line test. My reading of the 1999 WHO guidance is that less reliance should be placed on the OGTT than before, but this 10 minute consultation gives the message that the OGTT is still the preferred diagnostic test. Most patients attending our diabetes clinics with diabetes have been diagnosed on the basis of one or two fasting or random plasma glucose tests. I believe that the OGTT is most useful when impaired fasting glycaemia is found to persist on a repeat measurement. Competing interests: None declared