REAPPRAISAL OF THE HYPOOSMOTIC SWELLING TEST TO IMPROVE ASSESSMENT OF SEMINAL FERTILITY STATUS

The hypo-osmotic swelling (HOS) test has been proposed as a useful assay for evaluation of the functional competence of the human sperm membranes. To assess this further, the HOS-test was evaluated in 187 semen samples collected from fertile men and from male patients consulting for infertility. These samples were classified as normal, oligo-, astheno- or oligoasthenozoospermic on the basis of their standard semen variables. The percentage of total sperm tail swelling and of sperm exhibiting different tail swelling patterns was recorded. In the fertile men and in the group of patients with normal semen variables, significantly more (P < 0.001) HOS-reactive sperm were observed after hypo-osmotic treatment in comparison with those groups exhibiting abnormal semen parameters. Swelling of the sperm in a hypo-osmotic medium was highly correlated with both progressive motility (r = 0.62, P < 0.001) and sperm viability (r = 0.65, P < 0.001). A weak positive correlation was also observed between sperm swelling and sperm morphological features (r = 0.31, P < 0.005) and between sperm swelling and sperm concentration (r = 0.31, P < 0.005). No significant correlation was observed between sperm swelling and in-vitro sperm fertilizing capacity as assessed by the zona-free hamster oocyte penetration assay. However the majority of the semen samples (87.3%) showing a normal penetration rate (greater-than-or-equal-to 10%) also exhibited a 60% (or higher) reaction in the HOS-test. Finally, the results indicate that when the cut-off values for the rate of total swollen sperm and tail tip (B pattern) swollen sperm were set at 45% and 20% respectively, rates were above the cut-off value in all fertile and normozoospermic groups. These findings provide additional evidence of the worth of this assay in the evaluation of the subfertile men as a relevant part of a comprehensive male fertility assessment.