For example, in rheumatic fever, antibodies against group A streptococcal cell walls can also react with (and thus damage) human heart tissues.
Other options include the use of heterophile blocking reagents, steps to remove immunoglobulins, serial dilutions and using non-mammalian capture and/or detection antibodies.
[5] Heterophile antibody interference does not usually change linearly with serial dilution, but a true result typically will.
Heterophile antibodies are of particular importance in clinical medicine for their use in detecting Epstein-Barr Virus (the causative agent of infectious mononucleosis).
False positive monospot tests may occur in cases of HIV, lymphoma, or systemic lupus erythematosus.
There have been case reports where women have undergone an exploratory laparotomy for suspected ectopic pregnancy after having a falsely elevated beta-hCG test, only to find out later they actually have selective IgA deficiency.
Thus, another possible cause of false positives in a pregnancy test are heterophile antibodies, commonly seen in EBV infection as well as selective IgA deficiency.