Because doxycycline is an immunosuppressant and affects igg production. will it cause a false negative labcorp chemiluminescent treponema antibody test result testing for very late (10y)misdiagnosed/mistreated syphilis? pcp says no but worried?

You have found misinformation or misunderstood what you read or were told. Doxycycline does not have significant immunosuppressive properties and does not affect antibody response to syphilis or any other infection. Your PCP is correct: nothing causes false negative syphilis. This is your third (or fourth or more?) such question. Please stop asking on HealthTap.

Although some tetracyclines can modulate the immune system in some circumstances, doxycycline is not an immunosuppressant drug and will not affect the Lab test for syphilis. You should see your doctor or get a second opinion if you have further questions. Good luck.