The hypo-osmotic swelling test: Is it a sperm vitality or a viability assay?

Abstract

The first two editions of the World Health Organization laboratory manual described the determination of live spermatozoa by a dye exclusion method as a sperm ''viability'' test, whereas subsequent editions classified it as a ''vitality'' test, without providing an explanation for the reclassification. Additionally, the hypo-osmotic swelling (HOS) test, which assesses the functional integrity of the human sperm membrane, was placed in the same category as the dye exclusion test. Although the two terms might seem synonymous, the term ''vitality'' merely means ''alive,'' whereas ''viability'' assesses qualities or physiological functions of a living entity. After comparing the morphological, physiological, and clinical findings obtained from dye exclusion testing vs. the HOS test, we conclude that the HOS test should be classified as a viability test, not merely as a vitality test.

Hypo-Osmotic Swelling Test and Male Factor

“…There are many fertility specialists who think that the HOS test and sperm vitality are synonymous, or at least test the same thing. In fact, this is not true [21]. As expected, there were no males with subnormal vitality tests who had normal HOS test scores [20].…”

“…Although the two terms might seem synonymous the term "vitality" merely means "alive" whereas "viability" assesses qualities or physiological function of a living entity. After comparing the morphological, physiological and clinical findings obtained from dye exclusion testing vs. the HOS test, we concluded that the HOS test should be classified as a viability test, not merely as a vitality test" [21]. Whereas males with AOT would be likely to have both abnormal dye exclusion tests and low HOS test scores (a structural defect in the sperm membrane will lead to a functional defect as well), males with otherwise normal semen parameters are very unlikely to have an abnormal dye exclusion test, yet a low HOS test score is very possible.…”

“…As Drs. Hecht and Jeyendran point out, the HOS test is not synonymous with the sperm vitality or viability test [21]. Whereas all semen analyses with a structural defect of the sperm membrane, as evidenced by a subnormal viability (vitality) test, would have a low HOS test score, a functional defect of the sperm membrane, as evidenced by a low HOS test score, would not necessarily be associated with a structural defect.…”