My friend got tb skin test last three day. There is no swell spot or redness and the result of the test is negative. But on day 4, he start to have redness spot on the injection area and a bit itchy.

Does it mean he has tb virus?


First, tuberculosis is caused by a bacterium, not by a virus.

There are a number of different skin tests used for tuberculosis. The common ones are the Mantoux test, the tine test, and the no-longer-used Heaf test. All three of them indicate potential tuberculosis infection by measuring the presence and/or size of the firm raised area at the injection site after a certain amount of time; the NHS's instructions for administering the Mantoux test specifically call out itching of the injection site as normal, and state that any redness should be ignored when judging the results.

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