Defining the valid hemizona assay: Accounting for binding variability within zonae pellucidae and within semen samples from fertile males

Objective: To achieve a better understanding of the variability in sperm and oocyte binding capacities will optimize use of the hemizona assay (HZA) as a predictor of sperm function. Design: Limitations of the HZA were more clearly delineated by current studies: (1) variability of sperm binding capacity of men over a 90-day interval; (2) variability of sperm binding using different oocytes; and (3) lower limits of the number of sperm bound from the fertile control in two laboratories. Patients: Semen was obtained from proven fertile men and one subfertile individual. Main Outcome Measure: The number of sperm tightly bound to the hemizona were measured and compared. Results: In the initial study, 6 fertile control men exhibited a similar degree of variability in zona binding when studied over a 90-day interval. Average sperm binding for individuals ranged from 68 to 127. Second, 3 of the 15 simultaneous assays showed very low numbers of sperm bound, indicating that 20% of the zonae had poor binding. Third, from 18 men who had 0% fertilization in an in vitro fertilization system using mature oocytes, evaluation of their sperm by HZA was performed. The sperm bound poorly and the 95% confidence interval was 20 sperm bound. Thus, the fertile controls should bind >20 sperm to distinguish them from the infertile group in the HZA system resulting in a valid assay. Conclusions: With these guidelines, applications of the HZA may be made with greater reassurance of a valid bioassay of sperm fertilizing potential.