Sperm Penetration Assay (SPA)

Definition - What does Sperm Penetration Assay (SPA) mean?

A sperm penetration assay (SPA) is a lab test used to measure sperm ability to undergo capacitation— a set of physiological changes that sperm must undergo to be able to penetrate the egg and fertilize it. The test calculates the percentage of pretreated hamster eggs that are penetrated by human sperm. SPA is not frequently performed and is unlikely to significantly alter treatment recommendations.

Sperm penetration assay is also known as a hamster test, hamster penetration test, and zona-free hamster oocyte penetration assay.

FertilitySmarts explains Sperm Penetration Assay (SPA)

In order to predict the capacity of sperm to fertilize an egg, a sample of sperm is mixed with 15-20 prepared hamster eggs in a laboratory. The hamster eggs are chemically treated so that human sperm could penetrate them. The assay takes 3 hours after which eggs are analyzed. If less than 50 percent of eggs are penetrated, that means sperm has less capacity to fertilize a human egg. Whereas, a higher percentage of sperm penetrating the eggs is an indication of normal capacitation. Low penetration would indicate intracytoplasmic sperm injection (ICSI) as a method of fertilization during in vitro fertilization (IVF) treatment.

The results of the SPA vary over time and are sensitive to culture conditions. Even proven sperm donors are likely to fail the SPA as it has high false negatives, meaning the sperm fails to penetrate the hamster egg, but it does have the ability to penetrate a woman’s egg.

SPA is costly, time-consuming, cumbersome, and not widely available, which is why this test is rarely used.

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