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PAPERS: Josie M M Evans, Ray W Newton, Danny A Ruta, Thomas M MacDonald, Richard J Stevenson, and Andrew D Morris Frequency of blood glucose monitoring in relation to glycaemic control: observational study with diabetes database BMJ 1999; 319: 83-86 [Abstract] [Full text]

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Limitations of an observational study on blood glucose monitoring and glycaemic control

Helena Austin   (22 July 1999)

Limitations of an observational study on blood glucose monitoring and glycaemic control 22 July 1999
Helena Austin, 3rd Year Medical Student Newcastle University Medical School Send response to journal: Re: Limitations of an observational study on blood glucose monitoring and glycaemic control	We were interested to read the study by Evans et al. (BMJ 1999; 319: 83-86), in which data from a diabetes register were used to assess the relationship between use of glucose monitoring strips and blood glucose control. We have some concerns about the validity of their conclusions. The authors rightly allowed for a number of confounding factors. However, there may be many other differences between those using and not using the strips, which could explain the differences in glucose control observed. These include: intensity of insulin regime; frequency of follow- up and attendance; compliance with treatment and diets; and place of care (GP, hospital outpatients, or shared care). Even assuming that the differences in blood glucose control observed were not due to confounding factors, a problem of generalisability and possible selection bias remain. The subjects were a highly selected group: 790/5601 type II diabetics were considered eligible (with selection criteria not stated), and only 258 type I and 290 type II diabetics with a recorded glycated haemoglobin concentration were included. Hence the findings may not apply to other diabetics on the register We believe these findings from such observational studies should be treated with great caution and given the limitations it is unsafe to conclude that self-monitoring improves control. Evidence from more rigorous studies is required. Yours sincerely Helena Austin Stephen Metcalfe BMedSci (Hons) Helen Oliver Peter Yeates BMedSci (Hons) Patrick Yu-Wai-Man 3rd Year Medical Students Department of Epidemiology & Public Health, The Medical School, University of Newcastle upon Tyne