A semen analysis parameter that determines the percentage of spermatozoa with structurally intact cell membranes (live cells, whether motile or immotile) in an ejaculate sample. According to WHO criteria (6th ed., 2021), the normal reference value must be equal to or greater than 54%; lower values define a condition known as necrozoospermia. It is evaluated using supravital stains (e.g., eosin-nigrosin) or the hypo-osmotic swelling test (HOST).