How do you approach a positive Quantiferon/PPD test result in a patient for whom testing is sent without a clinical indication and who does not have a risk factor for TB exposure nor TB reactivation?

If a test for TB infection such as a Quantiferon or PPD is done without TB exposure risk factor or clincial indication and is positive, a chest X-ray and good history for symptom assessment and exam should be done. I will assess to see if there is an increased risk of developing TB such as an immunocompromising condition or treatment, or planned immunosuppressive therapy. If there is no risk factor for reactivation and normal exam and CXR, I usually educate the patient that the test is likely to be false positive and that no treatment is needed. The vast majority of the time, when the Qunatiferon value is low, a repeat test is usually negative, and sometimes a repeat is necessary for reassurance, both of the patient and the clinician.

Pre-test probability is key in TB/LTBI. T-Spot has been a good tiebreaker for me, but I’ve used it pretty much exclusively in situations of an indeterminate QFT. Again, pre-test probability. If still uncertain/unclear and risk of reactivation from, say, use of immunosuppressive medications, I try to treat and leave the option of not treating, of considering possible false positive if, for some reason, treatment is not possible, not tolerated/adverse effects, but, even then, would have to evaluate very carefully on a case by case basis. There’s also always the option of calling the local TB referral center for advice.

If conversion happens or risk factors are present then treat.