The diagnosis of azoospermia depends on the force of centrifugation

To determine the centrifugal force required to pellet sperm.

Prospective, in vitro study.

Tertiary referral center.

Men undergoing semen processing or postvasectomy semen analyses.

In Phase I, postvasectomy semen samples were centrifuged at 600 x g, and the pellets were examined. Supernatants from samples with no visible sperm underwent repeat centrifugation at 1,000 x g; the supernatants were removed and centrifuged at 3,000 x g. Pellets from both centrifugations were examined. Phase II examined nonazoospermic semen that was divided into 3 aliquots and centrifuged at 500, 1,000, and 3,000 x g. The supernatants were examined for the presence of sperm.

Sperm presence in centrifuged pellets or seminal supernatant.

Phase I: After centrifugation at 1,000 x g and 3,000 x g, sperm were noted in 12% and 0% of samples, respectively. Phase II: Sperm were noted in the supernatant in 100% of samples subjected to 500 x g and 1,000 x g, and in 92% of samples subjected to 3,000 x g centrifugation.

If sperm are in the seminal plasma, they will also be present in the pellet following centrifugation at a force of 1,000 x g or greater. Semen samples that appear azoospermic upon initial wet mount microscopy should be centrifuged at a minimum of 1,000 x g for 15 minutes.