mantoux test false positive readings

Question

Last year I got a mantoux test which showed a positive reading withing 30 minutes. Subsequent x ray showed nothing. I was born in Hong kong and was given TB vaccine and advised to ignore the positive. This year the same test showed the same result (swelling size of a quarter within 30 minutes) I am reluctant to take drugs in the event that this is a false positive. Is a false positive due to the vaccine or sensitivity to the test likely. I do not have HIV and am healthy. Picked up this site on a search for the Mantoux test. Your input still appreciated. Thanks

Answer

I will answer this since many people with HIV/AIDS have questions about the TB skin test (aka mantoux or PPD). The test is read by measuring the amount of swelling under the skin at 48-72 hours. An immediate reaction does not mean anything, and may be a reaction to the injection itself.

The BCG vaccine is given during childhood. It does NOT routinely cause false positive tests in adults, a common myth. For a few years after vaccination, positives can occur, but they are usually small reaction, often of less than 10 mm.

If anyone is reading your test at 30 minutes and not at 48 to 72 hours, they are confused. Make sure things are clarified

Good luck

ATP

Andrew T. Pavia, M.D.