Hypo-osmotic Swelling Test
When sperm are placed in a hypo-osmotic solution of sodium citrate and fructose, a normal sperm tail will swell and coil as fluid is transported across the membrane. Conversely, if there is a functional disturbance of the tail membrane, the tail will appear unaffected. This test has been scrutinized by a number of investigators with the weight of opinion denying an important role for the hypo-osmotic test. Not all types of swelling are fully correlated with sperm parameters and the SPA. The best correlation has been with significant swelling at the tip of the tail.

Measurement of Adenosine Triphosphate (ATP)
ATP is an important component of sperm metabolism. The levels of ATP in semen can be a strong discriminator between populations of fertile and infertile males. A multicenter study sponsored by the World Health Organization concluded, however, that levels of semen ATP could not predict the occurrence of pregnancy when the female partner was normal and the male partner had a sperm concentration greater than 20 million/mL.

Measurement of the Acrosome Reaction
The acrosome reaction (see Chapter 7) occurs on or near the zona pellucida. However, a little percentage of sperm will become reactive while in media or follittleing treatment with a calcium ionophore that induces capacitation. Although the initiation of the acrosome reaction has been correlated with IVF results, the relatively little difference in acrosome-reactive sperm in the different groups leaves one hesitant to suggest that this approach is clinically important.

Measurement of Acrosin
Acrosin is a proteolytic enzyme associated with the acrosome which may be important for aiding sperm to traverse the zona. Low acrosin concentrations could be associated with infertility. Difficulties associated with accurately measuring acrosin have limited its clinical applicability; however, an assay kit is now available for clinical use.