Analytical Techniques to Test Sperm Viability
The standard and recommended viability test for sperm is that recommended by the WHO manual. The test in effect identifies which sperm have an intact membrane by either excluding a particular dye or hypotonic swelling. Briefly, dye exclusion means that any damaged plasma membrane will allow entry of membrane impermeant stains; it entails a vitality test using eosin-nigrosin where live spermatozoa will have white heads and dead spermatozoa will be red. Eosin alone1 is also an option for testing viability. Some commercially available options are provided, for example, Sperm VitalStain from Nidacon, Sweden.
Unfortunately, the use of any stain precludes an individual sperm from being used clinically. Hence, the act of staining, although providing information about viability, will not be useful. Another test that is commonly used to assess viability is the hypo-osmotic swelling test (HOST), which acts because sperm with intact membranes are not leaky and will swell as they are able to retain fluid leading to coiling of the tail. The test was first described by Jeyendran et al.9 in 1984 and is a good indicator of the functional integrity of the sperm membrane.6 Its use in being able to select viable nonmotile sperm is popular because of the simplicity of the test. One problem with the test is that it may be less accurate when frozen-thawed spermatozoa are assessed as they experience a higher rate of spontaneously developed tail swellings and that this can exaggerate the HOST score.10