Body surface area and glucose tolerance - The smaller the person, the greater the 2-hour plasma glucose.

Background: The oral glucose tolerance test (OGTT) is standardized globally with a uniform glucose load of 75 g to all adults irrespective of body size. An inverse association between body height and 2-hour postload plasma glucose (2hPG) has been demonstrated. Our aim was to evaluate the relationship between body surface area (BSA) and plasma glucose values during an OGTT.

Methods: An OGTT was performed on 2659 individuals at increased cardiovascular risk aged between 45 and 70 years of age, who had not previously been diagnosed with diabetes or cardiovascular disease. Their BSA was calculated according to the Mosteller formula. Study subjects were divided into five BSA levels corresponding to 12.5, 25, 25, 25, and 12.5% of the total distribution.

Findings: When adjusted for age, sex, waist circumference, alcohol intake, current smoking, and leisure-time physical activity, BSA level showed an inverse linear relationship with the 2hPG in all categories of glucose tolerance (p for linearity < 0.001). Moreover, the smaller the adjusted BSA of the study person, the higher the proportion of newly diagnosed type 2 diabetes based on 2hPG in the OGTT.

Interpretation: Body size has a considerable impact on the findings from a standardized OGTT. Smaller persons are more likely to be diagnosed as glucose intolerant than relatively larger sized individuals.

Funding: This work was supported by the State Provincial Office of Western Finland, the Central Satakunta Health Federation of Municipalities, Satakunta Hospital District, and the Hospital District of Southwest Finland.

Research In Context: Evidence before this study. We searched PubMed using the MeSH terms "glucose tolerance test", "body surface area", "body height", "body size", "glucose tolerance", "insulin resistance", "blood glucose" and "diabetes mellitus" on March 10, 2019 without language restrictions. We also used Cited Reference Search in Web of Science for relevant articles. The oral glucose tolerance test (OGTT) is standardized globally with a uniform glucose load of 75 g to all adults irrespective of body size. An inverse association between body height and 2-hour postload plasma glucose (2hPG) has been demonstrated. Several studies have shown that 2hPG predicts all-cause mortality better than elevated fasting glucose. However, body height or body surface area are not usually adjusted in epidemiological studies. It is well known that short adult stature is a risk factor for cardiovascular and all-cause mortality. Added value of this study. This is the first study to assess the relationship of body surface area and 2hPG in a typical primary care population at increased cardiovascular risk. Body surface area has a considerable impact on the result of a standardized OGTT. Smaller individuals are more likely to be diagnosed as glucose intolerant than relatively larger sized individuals. Implications of all the available evidence. There is a possibility that the diagnosis of type 2 diabetes made by an OGTT is a false positive result in a relatively small individual, and a false negative result in a relatively larger individual. Association of 2hPG concentrations and mortality may be influenced by body size as confounding factor. Given that the OGTT is a time and effort consuming test both for patients and laboratory personnel, validity of the OGTT for different body sizes should be reconsidered.