Application of the hypo-osmotic swelling test to spermatozoa prepared by swim-up and discontinuous Percoll separation.

The quality of spermatozoa prepared by washing and swim-up or by discontinuous Percoll centrifugation, was compared by applying the hypo-osmotic swelling (HOS) test to semen samples from 116 men of infertile couples. The HOS test performed on 95 normal semen samples showed that the percentage of swollen spermatozoa separated by both techniques was significantly higher than in the initial ejaculate (p < 0.001). The percentage of HOS-positive spermatozoa separated by the Percoll gradient technique was significantly higher than that separated by the swim-up technique (p < 0.001). On the contrary, in 21 abnormal semen samples, there was no significant difference in the percentage of spermatozoa which were positive in the HOS test between the Percoll gradient and the swim-up technique (p = 0.44). It is suggested that the Percoll gradient technique appears to be preferable to the swim-up technique when semen parameters are normal, but there is no significant difference between these two technique in abnormal semen.