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Anti-Sperm Antibodies

Anti-sperm antibodies (ASAb) are due to an abnormal immune response to a man’s sperm, and this can significantly reduce his fertility. The antibodies adhere to sperm (because they recognise them as abnormal cells), and this encourages them the “clump” together, which reduces their motility and ability to fertilise eggs.

ASAb can affect either partner, but it’s much more likely to affect men, and it’s much easier to check for male anti-sperm antibodies with an extension of the standard semen sample.


Men normally have a barrier between their blood and their testes which physically separates their sperm from their immune system. If the immune system comes into contact with sperm, an immune response can be triggered that results in anti-sperm antibody production. Sperm only carry half the chromosomes and DNA of normal cells, which makes them “abnormal” to the immune system, and it responds by attaching antibodies to the cells. White blood cells search for antibodies, and they remove the cells that have them attached to them.

Any damage to the testes-blood barrier can trigger anti-sperm antibodies, and the usual causes are:

  • Infections
  • Torsion of the testes
  • Trauma (including surgery)
  • Varicocele

ASAb Rates

Anti-sperm antibodies affect a significant proportion of men with fertility issues:

  • Over 50% of men with low sperm motility carry ASAb i
  • About 66% of men with no live sperm carry ASAb ii
  • Up to 70% of men with a vasectomy or a vasectomy reversal have ASAb iii


There are a couple of ways to test sperm for their ASAb levels directly:

1. SpermMar Test

This is a relatively simple test that looks for IgG antibodies, and small latex particles that have been treated to detect ASAb are mixed with sperm. The results are based on the percentage of sperm that agglutinate (stick to each other) and the treated latex:

  • Negative: under 10%
  • Borderline: between 10 and 50%
  • Positive: over 50%

2. Immunobeads screen

This is a more complex test that can differentiate between the two forms of ASAb (IgA and IgG), which gives more information on where the antibodies attach to the sperm (head or tail), and the test is positive when over 20% of the sperm are affected.