Corea M et al. (2005) The diagnosis of azoospermia depends on the force of centrifugation. Fertil Steril 83: 920–922

The diagnosis of azoospermia is dependent on the manner in which the semen specimen is processed; severely oligospermic samples may appear to be azoospermic if the rare spermatozoa are not adequately concentrated. Corea and colleagues have carried out a two-part study of the centrifugal force needed to pellet sperm.

In the first part of the study, 25 semen samples were obtained from men who had undergone vasectomy. These samples were judged to be azoospermic following standard microscopic examination. After centrifugation at 600 × g for 10 minutes, none of the resulting pellets contained visible sperm. When the supernatants were further centrifuged at 1,000 × g for 15 minutes, however, sperm were observed in 3(12%) of the new pellets. A third round of centrifugation—at 3,000 × g for 15 minutes—failed to identify any new oligospermic samples.

In part two of the study, semen samples from 25 nonazoospermic men were divided into three aliquots and centrifuged for 15 minutes at 500, 1,000 or 3,000 × g. Microscopic examination showed that motile sperm remained in all of the resulting supernatants, except for two of those that had been centrifuged at 3,000 × g. Thus, it was not generally feasible to separate all sperm from the seminal plasma using a standard clinical centrifuge.

In conclusion, the study showed that sperm may remain in the supernatant even after centrifugation above 1,000 × g. To distinguish between azoospermic and oligospermic samples, the authors recommend centrifugation at a minimum of 1,000 × g for 15 minutes.