Chlamydia trachomatis IgA antibodies in serum (Chlamydia trachomatis Abs IgA, Serum) is a blood test used to detect IgA antibodies produced by the immune system in response to infection with Chlamydia trachomatis. This test helps determine whether a person has been exposed to an active or past infection with this bacterium, which causes genital infections that can lead to conditions such as infertility. It is also used in some cases to diagnose urinary tract infections or pelvic infections caused by this bacterium.