A quality control system for the optimized sperm penetration assay.
OBJECTIVE: To develop a quality control system for the optimized sperm penetration assay (SPA) and to use this system to monitor interassay variability and stability over time. DESIGN: Four semen donors were tested consecutively for a period of weeks (7 to 139 weeks) with the SPA. Their average semen analyses and SPA scores were evaluated to monitor natural biologic variation. Intra-assay variation was obtained by dividing 11 semen samples into three aliquots and testing each separately in the SPA. A single ejaculate from seven individuals was aliquoted and frozen to be used as a control. They were tested on different assay days in 1986 and subsequently in 1991 to evaluate the assay stability over time. MAIN OUTCOME MEASURES: Results were expressed as a sperm capacitation index (mean number of sperm penetrations per ovum). RESULTS: Consecutive weekly semen analyses and SPAs on donors exhibited coefficients of variation ranging from 20% to > 40%. In contrast, these variations were much greater than intra-assay variability. Analysis of frozen semen specimens tested in several SPAs also displayed a low coefficient of variation. When aliquots of these frozen samples were tested in the SPA 5 years later, there were no differences in the observed values, showing the remarkable stability of this assay over time. The lower limit of the normal fertile range did not change over a period of 2 years. CONCLUSIONS: Results show that using fresh semen samples as a positive control in the SPA is inadequate. This deficiency has been overcome with the use of frozen semen controls. With frozen semen for quality control, the optimized SPA developed in this laboratory is a highly reproducible assay that meets the strict criteria required for clinical laboratory certification.