Thursday, December 27, 2007

Sperm Penetration Assays (SPA, "Hamster Tests")





There have been many attempts made to develop a Laboratory test that will accurately predict the ability of a human sperm to fertilize a human egg. Dr. Aitken and his group many years ago demonstrated a correlation between sperm movement characteristics and sperm fertilizing ability as evaluated by the zona pellucida-free hamster egg penetration test. In this test, the species specific barrier to penetration (not fertilization) is removed from the ova (eggs) of the hamster. These oocytes are then exposed to prepared sperm from the man being tested. 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. There is some feeling that if a man's sperm are able to penetrate the hamster eggs in the laboratory, there is a higher likelihood that his sperm will ultimately be able to fertilize a human egg if so exposed. This test is not uniformly accepted, due to the high false negative (no penetration of the hamster egg, but wife gets pregnant anyway) rate and the sometimes seen false positive (penetrates the hamster egg but does not fertilize human eggs in vitro) rate of this test. Global experience has been that good performance in the hamster test can provide some limited reassurance of the likelihood that a man's sperm will be able to achieve fertilization if given the chance. If men fail the hamster test, most centers rely upon in vitro fertilization with ICSI. This protocol has provides excellent success rates in men whose sperm function remains questionable. It should be noted that most men that fail the hamster test, are able to achieve normal fertilization with ICSI.

Wednesday, December 26, 2007

Computer Assisted Semen Analysis (CASA)



The use of computer asisted semen analysis has advanced the ability to study and understand sperm function as it relates to human infertility. The major advances have been in the ability to more accurately determine sperm concentration (counts) and motility (movement). Generally, sperm are "looked" at by a computerized digitizing tablet through a microscope. The computer has been "taught" by the laboratory personnel what sperm look like, and how they move. When the computer then "sees" a sperm under the microscope, it is able to draw a digitized picture of each individual sperm, including the speed and path this sperm takes while moving under the microscope. A great deal has been learned about the normal and abnormal "micro"characteristics of sperm employing this method. The method is, however, not foolproof. The computer is only as intelligent as it's programmer. Small changes in the computer program can alter the sperm calculations significantly. The computers must constantly be monitored and updated. In most laboratories, all grossly abnormal CASA assays are always verified by both a repeat analysis as well as with a "hands on" human second look opinion. We feel that any abnormal sperm count must be verified by a manual counting and assesment method.