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Thermometer rising CMAJ 2000;163(4):387 In response to: S.C. Arya See also: We agree with Subhash Arya that ambient temperature during an oral glucose tolerance test might be another important determinant of outcome. However, the findings of Schmidt and coworkers,1 which form the basis of this suggestion, are complicated by several factors. Their analysis involved pregnant subjects, was observational (temperature was measured, not controlled) and did not differentiate between the effects of acute and chronic ambient temperature. Three earlier studies that investigated differences in blood glucose levels at 2 clinically controlled temperatures (23°C v. 33°C) in nonpregnant subjects are more directly applicable.2,3,4 All 3 support the findings of Schmidt and coworkers,1 demonstrating that an increase in ambient temperature increases 2-h plasma glucose levels after a 75-g oral glucose tolerance test. To avoid the possibility that changes in ambient temperature might confound our results, the temperature is controlled in our clinic by a thermostat set at 22°C and subjects acclimatize for a minimum of 15 minutes before commencing testing. The blood glucose raising effect of dilution we observed at 30, 45 and 60 minutes and for the area under the curve, therefore, is relevant for this temperature [Research].5 Whether our observations at 22°C would hold at higher or lower temperatures is unclear. Temperature should not interact with the effect of dilution, provided the temperature is constant for each dilution. There is no direct evidence to suggest that the gastric-emptying mechanism, by which dilution is thought to increase glycemia, is influenced by ambient temperature within normal testing limits, although cold stress might affect gastric emptying.6 It would be interesting to explore the interaction between the effects of temperature and dilution on postprandial glycemia in a further study, but such a study likely would not yield practical results. It is probably sufficient to be aware that both of these factors affect the outcome of oral glucose tolerance testing. In this regard, attempts might be considered to standardize ambient temperature and account for its effects when comparing across centres. The same might be considered for dilution when using oral glucose tolerance testing criteria that rely on intermediate time points for diagnosis, as these points, but not 2-h postprandial glucose levels, appear to be sensitive to alterations in dilution.5
John L. Sievenpiper References
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