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Additional, Advanced Sperm Testing Procedures
Many of the following tests are found useful at The Fertility Institutes
in our investigations of males who have demonstrated "problem" results on
earlier semen analysis. These tests are not performed routinely in the initial
testing of sperm, but are employed to help further understand the nature
and extent of a possible sperm or semen "problem".
Hypo-osmotic swelling (HOS) test
This fairly simple and relatively inexpensive test is based on the
semipermeability (ability to allow fluid or elements to pass through it's
membrane) of the intact sperm cell. A live sperm cell will "swell" when placed
in a solution that is "hypo-osmotic", expanding the cell's volume. This test
is easy to score and provides valuable information on the integrity and behavior
of the cell membrane of the sperm tail.
Zona-free hamster oocyte test
One of the most widely used accessory tests in the evaluation of advanced
sperm function, the fusion between human sperm and the hamster oocyte (egg)
is nearly identical to that occuring with the human egg. Fusion with the
vitelline membrane of the oocyte is normally initiated by the healthy sperm's
plasma membrane that lies over a special section (equatorial segment) of
the sperm head in a sperm that has prepared itself for normal fertilization.
This test relies upon the ability of sperm that are tested in the laboratory
to undergo the necessary reactions to fertilize an egg. Because the sperm
prepare themselves in a slightly different manner in the laboratory than
in the body, false negatives (fail in the hamster test but normally fertilize
the partner's human egg) have been reported. This test may be used as a screen
to asist in determining which men may need the assistance of
"ICSI" fertilization by our embryology team.
Reactive oxygen species and male infertility
Reactive oxygen species in the sperm result from the metabolism of oxygen
by the sperm cell. These species include superoxide anion, hydrogen peroxide
and nitric oxide. The detection of excess amounts of these chemicals in the
sperm combined with abnormally high concentrations of certain enzymes may
indicate that the involved sperm are immature, damaged or abnormal. Excess
levels of reactive oxygen species can produce oxidative damage to important
components of the sperm. Sperm normally maintain levels of "anti" oxidant
systems to protect the sperm cell. If the presence of high levels of oxidants
are present, the cell's defenses may be overwhelmed, and cellular damage
may result. Chemiluminescent testing in the laboratory can detect excess
levels of reactive oxygen species.
Zona pellucida binding tests
When a normal sperm binds to the zona pellucida of a healthy egg, the sperm
normally undergoes an "acrosome reaction" that releases components that lead
to normal fertilization. This process may be approximated in the laboratory
by exposing the sperm being tested to the dissected zona pellucida of human
eggs obtained from non-fertilized human eggs. The zona pellucida of such
an egg is split in half. Sperm from the man being tested are exposed to one
half of the split zona pellucida, while sperm from a man known to have
"normal-fertile" sperm are exposed to the other half. A comparison of the
performance of the sperm of the two men is carried out to ascertain the
functional binding capacity of serm of the man being tested.
Anti-sperm antibodies
Sperm antibodies in semen belong almost entirely to two classes of antibodies;
IgA and IgG. IgA antibodies are probably more important sources of sperm
problems than IgG. IgM antibodies, because of their large molecular size,
are rarely seen in semen. Of import, it has been found in the IVF labortory
that unless 50% or more of the sperm have antibodies coated on them, there
is little chance that the sperms function will be significantly impacted.
That is, problems are rarely encoutered from antibody levels lower than 50%.
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