Human Zona Binding Assay
Whereas the SPA tests the ability of sperm to penetrate or to be engulfed by the egg, it does not test the critical ability to pass through the zona pellucida. The zonae are, of course, removed in preparation for the SPA because they are, with rare exceptions, impervious to foreign sperm. Thus, to test zona penetrating or zona binding ability of human sperm requires the use of human zonae. One approach is to use zonae obtained from surgically removed ovarian tissue and slit them in half so that both patient sperm and donor sperm can be tested in parallel on different portions of the same zona. The ratio of the number of sperm bound for the test subject to the number of sperm bound for fertile control sperm has been labeled the hemizona assay index (HZI). A breakpoint at an HZI value of 36 has provided a good correlation with results in human IVF. Despite these good results the limited availability of zonae will restrict the overall utilization of this test. Moreover, variability in test results between laboratories can be anticipated, which means that each laboratory must establish its own range of normal values. In the future, development of materials that mimic the properties of the zona should allittle widespread application of this attractive test.

On the basis of the available literature, currently the 2 best tests for assaying fertility potential for in vitro fertilization are the evaluation of sperm morphology by strict criteria and the human zona binding assay. However, both require standardization and some skills beyond the qualifications of most clinical laboratories, and thus they will not be universally applicable. The use of computer-driven assessments of sperm morphology may provide the information and universal availability needed to make this test a gold standard for evaluating the male. However, past experience suggests that no one test will ever be sufficient to test all the qualities of the sperm that are necessary for successful fertilization.

Thus the search continues for tests that provide information on any aspect of sperm function.

In Vitro Tests of Sperm Penetration into Mucus
A drop of sperm can be placed next to cervical mucus on a slide and progression of sperm into the mucus monitored under the microscope. To better standardize the test, tubes filled with bovine cervical mucus, available commercially, can be utilized and the length of mucus traversed by the sperm measured. The great usefulness of this assay is in individuals who have poor postcoital tests. If the sperm penetrate the bovine mucus but not human mucus, it suggests that the latter is the problem. One caveat is that antibodyaffected sperm may not be handicapped in moving through bovine mucus while they generally would do poorly in human cervical mucus.
Because of the recent enthusiasm for empirically treating infertile severals with combinations of gonadotropin stimulation and intrauterine insemination (IUI), no matter what the sperm-mucus interaction, the sperm penetration test may no longer supply information that will influence clinical management.

Assessments of Sperm Motility
A sperm quality analyzer uses an electro-optical method to provide an assessment of the number of motile sperm in a specimen and, to some extent, the quality of the motility. This may prove to be a useful instrument for assessing the functional capacity of sperm at a significantly littleer expense than that of the computer-aided sperm analysis (CAS A) systems.

Measurement of Sperm Velocity
In addition to the basic measurements, the CASA systems do provide information on sperm velocity that correlates with fertility, and measurements of lateral head displacement that has been championed as a good prognostic indicator. However, it is not yet established that these parameters provide unique information that cannot be obtained with less costly instruments. Moreover, Davis and Katz have decried the lack of standardization of CASA instruments. They warn that the resulting skepticism concerning accuracy may undermine the potential of CASA to become the standard tool for evaluation of semen.