Comparison of testosterone fractions in Framingham Heart Study subjects and Japanese subjects Running title Comparison of testosterone fractions

Objectives: To determine testosterone fractions in Japanese men and to compare the values as stratified by age with those of Framingham Heart Study (FHS) subjects. Methods: We enrolled 498 healthy Japanese men. Total testosterone (msTT) was assayed by LC-MS/MS, sex hormone-binding globulin (SHBG) was assayed by immunoassay and free testosterone (cFT) was calculated by a lab at the Boston Medical Center. Analog FT (aFT) and total testosterone (iaTT) were determined by immunoassay. We compared msTT and cFT values in the Japanese subjects with values in the American FHS generation 3 cohort. Results: The mean serum msTT, SHBG and cFT values were 439.4±167 ng/dL, 65.34±30.61 nmol/L and 58.75±20.0 ng/dL, respectively. The correlation coefficients with age for msTT, SHBG and cFT were 0.0010, 0.5041and -0.496, respectively. There were no age-related changes in msTT values in healthy men (P=0.981), while SHBG and cFT levels showed similar age-related changes (P<0.0001). Serum aFT levels (8.24±12.9 pg/mL) showed age-related changes (P<0.0001) regardless of iaTT levels (P=0.828). Serum iaTT values (486.1±1162.5 ng/dL) correlated with serum msTT values