[The natural history of sperm cleareance after vasectomy]

To study the time required to obtain a negative sperm analysis after vasectomy.

We reviewed 239 consecutive vasectomies performed between september 1998 and september 1999. All of them were done in an ambulatory basis. Follow up interval was 41-853 days (mean 144, median 104). The first semen analysis was requested between 1 and 6 months after the surgical procedure. If the sample still showed spermatozoa, then a new one was requested every two months. Probability of becoming azoospermic was studied with Kaplan-Meier curves.

Persistent spermatozoa could be found in 31 patients (13%) at the end of follow-up. Despite having a positive semen analysis, 10 patients (4.2%) discontinued medical visits. Time required to obtain a negative sperm count ranged from 58 to 362 days (mean 133, median 99). The probability of being azoospermic 200 and 260 days after vasectomy was 80-90% respectively. A total of 328 semen analysis were requested (range 1-4, mean 1.37, median 1)

A minimum of 200 days (6.6 months) are needed to clear all the spermatozoa in semen after vasectomy in 80% of our patients. Requesting the first semen sample 7 months after vasectomy is cost-effective, reducing unnecesary medical visits and increasing the rentability of this test.