This study says that calculated free testosterone is associated with the symptoms of sexual dysfunction, while total testosterone was not. The study group was divided into four subgroup. with normal/low total testosterone and calculated free testosterone. They then filled out a questionnaire on sexual symptoms. Only the groups with low calculated free testosterone reported symptoms. The report says:
Data from 485 men were analyzed. Comorbidities were scored with the Charlson Comorbidity Index (CCI). Patients completed the International Index of Erectile Function (IIEF) and the Beck Inventory for Depression (BDI). Descriptive statistics tested differences between patients with normal TT levels (>3 ng/mL) and normal cFT levels (>65 pg/mL; group 1) and men with normal TT and low cFT (group 2), low TT and normal cFT (group 3), and low TT and low cFT (group 4). Linear regression models tested the association between clinical predictors and sexual function impairment.
Low cFT and normal or low TT achieved independent predictor status for pathologic IIEF domains and BDI scores after accounting for age, CCI, and body mass index. Conversely, low TT and normal cFT status was not associated with pathologic scores on the questionnaires.