Mantoux test, also known as Tuberculin Skin Test (TST) , Tuberculin Sensitivity Test, Purified Protein Derivative test (PPD test) is a screening test to detect TB. In this test, a little amount of the PPD is injected in the arm just below the skin. If a person has been exposed to the bacteria before, the immune system will cause a reaction to the injected bacteria. Based on the extent of reaction to the bacteria, the affected is diagnosed as exposed to TB.
The test liquid is injected in your forearm intradermally (that is, between the layers of skin). What this means is that the needle will not penetrate deep, will not touch the veins. It is only on the skin, just underneath the skin.
After 2-3 days, the induration is checked for its size. Based on the designated norms for the expected size, the results are positive, negative or doubtful for TB.
How does it feel:
Since the injection is intradermal, it just feels like a prick. Doesn’t pain at all despite the weakness and sensitive nerves from a (EP)TB infection. You could however experience itching and uneasiness. But resist scratching the spot as it could hamper results.
The Mantoux test was performed twice on me. Once 1 month after I developed pain in my back and right leg and the second time 5 months later. The first time Mantoux test was performed, I got an induration measuring 10mm. Their scales read:
Positive >10 mm
Doubtful 5-9 mm
Negative <5 mm
It was taken as a doubtful case and the diagnosis was not pursued. This was despite the fact that my ESR at that time was 62. ESR (erythrocyte sedimentation rate) or commonly “sed rate” hints at inflammation in the body. Normal ESR ranges have an upper limit of 15-20. High ESR (62) was clearly an indication of inflammation and infection, tuberculosis included as a possibility.
The second Mantoux test was performed when the spinal and sacral tuberculosis were more or less confirmed. Knowing that the previous Mantoux test had proved inconsequential, the nurse administered the liquid deep in a keen attempt to get a positive result. The injection was pushed in forcefully, to what I felt was a farther extent than the usual penetration level of the needle during a blood test. It didn’t help that I was weak and my nerves were jittery from the pain of past several months. This time it pained a lot and the arm ached for a couple of days. I don’t have the results of this test with me presently, so am unable to comment on it. But, the test is technically not supposed to be a deep inject. It is intradermal and the results need it to be intradermal. It may not be dangerous to inject the liquid in deep, but it fails the result and causes a lot of unnecessary pain.
My induration at that time looked similar to this representative image. I might be wrong here, but the skin in the region of the second Mantoux test still looks slightly different from the rest of the forearm.
The results are only indicative:
A false positive could occur because of allergic reactions or latent TB in the body. A false negative could also result from a reduced response of the immune system or a BCG vaccine. In all, the test is to be taken as indicative and not conclusive. Correlation with other results and further tests are needed for a complete diagnosis.