What are the normal readings for Mantoux test?
Induration size of 5mm and above are usually considered positive
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The( Mantoux test ) tuberculin skin test is one of the few investigations that are still widely used as an important test for diagnosing tuberculosis. Though very commonly used by physicians worldwide its interpretation always remains difficult and controversial. Various factors like age, immunological status coexisting illness etc influence its outcome, so also its interpretation.
There is no correlation between the size of induration and likelihood of current active TB disease but the reaction size is correlated with the future risk of developing TB disease.
If the induration exceeds 5mm, it is cosidered positive and there are different set of conditions which bring out different induration sizes like 10mm and 15mm etc..
On the other hand, a negative test does not always mean that a person is free of tuberculosis. People who have been infected with TB may not have a positive skin test (known as a false negative result) if their immune function is compromised by chronic medical conditions, cancer chemotherapy, or AIDS. Additionally, 10%-25% of people with newly diagnosed tuberculosis of the lungs will also have a negative result, possibly due to poor immune function, poor nutrition, accompanying viral infection, or steroid therapy. Over 50% of patients with widespread, disseminated TB (spread throughout the body, known as miliary TB) will also have a negative TB test.
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