Associations of free testosterone and estradiol levels with Int.vBMD and vertebral strength in AN with current amenorrhea. Among women with low-weight AN and atypical AN with current amenorrhea, (A, B) Int.vBMD and vertebral strength were positively associated with free testosterone levels. Among AN subjects with current amenorrhea, (C) Int.vBMD trended toward a positive association with estradiol levels, and (D) vertebral strength was not associated with estradiol levels. Values of (A, B) free testosterone and (C, D) estradiol are displayed on log-transformed axes. Regression lines were log-transformed with respect to (A, C) Int.vBMD, (A, B) free testosterone, and (C, D) estradiol. In multivariable models controlling for estradiol, age, and BMI among amenorrheic AN subjects, free testosterone remained significantly associated with vertebral strength (P = 0.01) and explained about 21% of the variability in vertebral strength, whereas estradiol was not associated with vertebral strength.