I had to get a pre-employment TB test yesterday, and when I filled out the paperwork, I was asked if I have an autoimmune disease. In fact I do-- autoimmune hemolytic anemia. The nurse said that I would be ineligible for the Mantoux TB skin test and would have to reschedule a blood test.
Does the Mantoux test inject living pathogens into the patient? What’s the contra-indication?
You’re more likely than the general population to have a false-positive test if you have an autoimmune disorder. They’ll schedule a blood test with greater accuracy.
It’s complicated. But first, know that TST (TB skin test, or Mantoux test) does not involve using any living TB pathogens, it’s a purified protein derivative.
Patients with autoimmune disorders test positive for TB with the TST more often than they do when tested with other modalities like Quantiferon blood testing. It’s still not exactly clear if this is due solely to false positive results or not, as there’s some thought that having a TB infection makes one more prone to autoimmune disorders in the first place. And meanwhile, autoimmune disorders can also result in the production of markers in the blood which also react with the TST. In addition, drug treatment for autoimmune diseases can also result in more TST reactivity. So it’s hard to know just what is going on with a patient with autoimmune disease plus a positive TST. If the patient has an active TB infection in the lungs (TB is busy reproducing and damaging the lungs) that can generally be determined by taking a chest x-ray and culturing sputum for TB. But if the TB infection is elsewhere in the body, or if it’s latent infection (TB is in there, but dormant and not reproducing) that can be harder to figure out.
So it’s generally better to get the quantiferon blood test in most (but not quite all) circumstances for autoimmune disease folks. Neither test is perfect, and there’s a lot of grey areas but I’d have a fair degree of confidence in the blood test in autoimmune situations.
Thank you @Qadgop_the_Mercotan for the thorough and helpful explanation!