Submitted on July 13, 2006
Accepted on January 30, 2007
Estimation of 
-cell function from the data of the oral glucose tolerance test
Shinji Sakaue1*, Shinji Ishimaru1, Daisuke Ikeda1, Yoshinori Ohtsuka2, Toshiro Honda3, Jun-ichi Suzuki3, Yoshikazu Kawakami3, Jun Ishii4, and Masaharu Nishimura1
1 First Department of Medicine, Graduate School of Medicine, Hokkaido University, Sapporo, Japan
2 Health Regulation Center, Hokkaido University, Sapporo, Japan
3 Division of Internal Medicine, Kohnan Hospital, Sapporo, Japan
4 Division of Diabetes and Metabolic Disease, Hokkaido Hospital for Social Health Insurance, Sapporo, Japan
* To whom correspondence should be addressed. E-mail: sakaue-s{at}med.hokudai.ac.jp.
Although a hyperbolic relationship between insulin secretion and insulin sensitivity has been shown, the relationship has been often questioned. We examined the relationship using oral glucose tolerance test (OGTT)-derived indices. A total of 374 Japanese subjects who had never been given a diagnosis of diabetes underwent a 75-g OGTT. In subjects with normal glucose tolerance (NGT), the ln[insulinogenic index (IGI)] was described by a linear function of ln(x) (x, insulin sensitivity index) in regression analysis when the reciprocal of the insulin resistance index in homeostasis model assessment (HOMA-IR), Matsuda’s index, and oral glucose insulin sensitivity (OGIS) index were used as x. Because the 95% confidence interval of the slope of the regression line did not necessarily include -1, the relationships between IGI and x were not always hyperbolic, but power functions IGI x x
= a constant. We thought that IGI x x was an appropriate 
-cell function estimate adjusted by insulin sensitivity and referred to it as -cell function index (BI). When Matsuda’s index was employed as x, the BIs were decreased in subjects without NGT. LogBI had a better correlation with fasting plasma glucose (PG)(FPG) and 2-hour PG in non-NGT subjects than in NGT subjects. In subjects with any glucose tolerance, logBI was linearly correlated with 1-hour PG and glucose spike (the difference between maximum PG and FPG). In conclusion, the relationship between insulin secretion and insulin sensitivity was not always hyperbolic. The BI is a useful tool in the estimation of -cell function with a mathematical basis.
