Sperm Penetration Assay
Sperm penetration assay overview
- Sperm penetration assay (SPA) analyzes the ability of a man’s sperm to bind or attach to the egg membrane, penetrate the egg and undergo decondensation. These are necessary first steps of actual fertilization.
- In SPA, also known as the “hamster test,” a man’s sperm is mixed with hamster eggs that have been pretreated with enzymes to remove the zona pellucida in a laboratory. Measuring the sperm’s ability to penetrate the pretreated hamster egg gives information about the sperm’s chances for penetrating a woman’s egg.
- The SPA is not an unconditional test for fertility because it does not analyze other aspects of sperm function.
What is the sperm penetration assay?
The sperm penetration assay (SPA), also known as the “hamster test” or “hamster egg penetration test” (HEPT), is a laboratory test to predict the capacity of a man’s sperm to fertilize a woman’s egg. In a laboratory sperm is joined with prepared hamster eggs. The number of penetrated eggs is measured to ensure the sperm is undergoing the necessary physiologic changes for fertilization.
The hamster eggs are chemically treated to allow normal human sperm to penetrate them. Prepared sperm are incubated with 15-20 hamster eggs; if the sperm is functioning correctly, it will be able to penetrate the eggs. The assay is stopped after three hours and all the eggs are fixed on glass slides for analysis.
Less than 50 percent of eggs penetrated may mean that the sperm has limited capacity to fertilize. If the penetration is above 50 percent, however, the sperm should have fertilization capability. If the penetration count is low, a physician may recommend intracytoplasmic sperm injection (ICSI) during in vitro fertilization (IVF) treatment.
When is the sperm penetration assay used?
The SPA is useful in analyzing sperm function in males who have unexplained infertility with normal sperm evaluation. It can also help determine if poor penetration ability is the reason that a man’s semen analysis is abnormal.
Often, the SPA is used prior to IVF to ensure proper sperm functioning with good quality before use for the fertilization of human eggs. SPA may also help determine whether ICSI is required to assist in fertilization.
Accuracy of the sperm penetration analysis
The SPA is not an absolute determinant for fertility potential because it does not analyze other important aspects of sperm function, such as movement, number and proper shape. The SPA test can also return a false negative, for example, indicating the sperm does not penetrate the hamster egg when the sperm can in fact fertilize a woman’s egg.
Risks of sperm penetration analysis
There are typically no risks associated with sperm penetration assay, as the collection of the semen sample is provided by masturbation. In cases of men who cannot ejaculate, sperm can be surgically retrieved, which carries the normal risks associated with surgery.