Right testicular volume is a dominant predictor of testicular function determined by sperm parameters and total testosterone.

This study aims to evaluate the predictive value of left testicular volume (LTV) and right testicular volume (RTV) for testicular function respectively. Men who requested fertility testing for any reason were enrolled from December 2012 to November 2015. Subjects with primary scrotal diseases or a condition interfering reproductive system were excluded. Testicular volume (TV) was evaluated by scrotal ultrasound. Sex hormone and semen analysis including sperm concentration (SC) and sperm motility rate (SMR) were performed. Statistical analysis including comparison, stepwise linear regression and logistic regression was used. Two hundred and seventy-four patients with oligoasthenozoospermia/low testosterone and 27 control subjects were enrolled. Both LTV and RTV positively correlated with testicular function, and no differences were found between bilateral TV. RTV is the best independent factor associated with testicular function determined by SC (β=.292, p < .001), SMR (β=.227, p < .001) and total testosterone (TT) (β=.245, p < .001). Using a RTV value of 15.47 ml, the highest discriminating sensitivity and specificity were 66.7% and 62.4% respectively. RTV (<15 ml) was the only positive predictor for low testicular function (odds ratio=2.79, 95% confidence interval: 1.18-6.66; p =.020). RTV rather than LTV is the independent factor of overall testicular function determined by semen quality and TT levels. Further studies are needed to support and elucidate the difference in volume-function between bilateral testes.