Sperm that have initiated apoptosis are destined to die. Therefore, these sperm would most likely not give rise to a viable embryo if used in assisted reproductive technologies (ART). Because of this, a method has been developed to discard apoptotic sperm from a semen sample before using them in ART, the MACS technique.
One of the first changes that spermatozoa that have initiated apoptosis undergo is the externalisation of phosphatidylserine. Thus, detecting this change in the membrane of apoptotic spermatozoa would make it possible to differentiate them from healthy spermatozoa, which is precisely what the MACS technique does. It uses annexin V (a protein that binds with high affinity to phosphatidylserine) and magnetic fields.