Introduction: Functional assays versus cell markers

Physicians and scientists dealing with the practical aspects of male infertility are driven towards the goal of identifying why the spermatozoa from a particular man have not achieved fertilization (diagnostic) and whether the sperm from a particular man have the capacity to fertilize an egg (prognostic). Furthermore, the information gathered will, it is hoped, lead to a therapeutic strategy for correcting or bypassing spermatozoal defects. The information at these three levels (diagnostic/prognostic/therapeutic) must come from quantitative and qualitative analysis of either cell markers or assays of sperm function. Cell markers differ from sperm functional assays, particularly in their contribution to clinical decision-making.

Evaluation of sperm markers gives information about the presence of a cellular factor, anatomic feature or cell response. The test yields a yes/no answer, or quantitates the level or concentration of the marker. These data allow the investigator to conclude that the patient is similar to fertile men or, conversely, similar to subfertile populations with respect to the marker. Today, examples of cell or fertility markers include: sperm viability, sperm density, percent motility, morphology, grade of progression (on a scale of 1 to 4), mean velocity, mean head amplitude (ALH), hyperosmotic swelling of the flagellar membrane (HOS), intracellular ATP concentration, level of creatine phosphokinase and presence of intact acrosomes. Acceptable levels of these markers have a direct or indirect relationship to necessary sperm functions. For some of these cell markers, it is obvious that its complete absence precludes normal fertilization (e.g. lack of motility or complete absence of acrosomes).