Flow cytometry sperm apoptosis test can predict sperm DNA fragmentation and can be used as an effective and easy-to-perform screening method for males from infertile couples.

BACKGROUND: Conventional sperm analysis is the gold standard for male fertility assessment. However, since the basic examination consists of microscopic evaluation of native ejaculate, some sperm pathologies might be missed during this examination. The sperm DNA fragmentation test is currently considered the most precise indicator of the sperm potential to fertilize an oocyte both naturally and by assisted reproductive technologies (ART). Irrespective of which method is used, sperm DNA fragmentation testing requires special technical equipment and chemicals together with skilled laboratory staff, and is usually time-consuming and costly. The primary aim of the presented study was to assess whether the flow cytometry sperm apoptosis test (FACS-APO) can predict sperm DNA fragmentation as measured by the terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay.

METHODS: In this retrospective observational study, we analysed 971 semen samples from 688 men who underwent concurrent conventional sperm analysis, FACS-APO, and TUNEL-based sperm DNA fragmentation testing at a single in vitro fertilization centre between January 2019 and December 2024. Non-parametric Spearman correlation and Kruskal-Wallis tests were used to assess associations between sperm DNA fragmentation, FACS-APO parameters, and conventional sperm analysis variables. A linear regression model predicting sperm DNA fragmentation from age and the percentage of viable sperm on FACS-APO was developed, and its diagnostic accuracy for a 20% sperm DNA fragmentation cut-off was evaluated.

RESULTS: A significant correlation was found between the percentage of sperm DNA fragmentation and the percentage of late apoptotic/necrotic sperm (ρ=0.38, P<0.001), and a significant negative correlation was found between the percentage of sperm DNA fragmentation and the percentage of viable sperm (ρ=-0.39, P<0.001). The correlation between the percentage of sperm DNA fragmentation and the percentage of early apoptotic sperm was less significant (ρ=0.10, P=0.002). Among conventional sperm analysis parameters, sperm concentration, total sperm count, and progressive motility each showed a significant correlation with sperm DNA fragmentation (P<0.001). A simple linear model for calculation of sperm DNA fragmentation was created: sperm DNA fragmentation (%) = 23 + 0.32 × age (years) - 0.35 × viable sperm (%). Based on this model, males at higher risk of having high levels of sperm DNA fragmentation might be selected, which ultimately may save substantial time and financial resources.

CONCLUSIONS: The flow cytometry sperm apoptosis test is an inexpensive, accurate, and easy-to-perform method and might be used effectively as a screening tool to select males at higher risk of having high levels of sperm DNA fragmentation.