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Monday, January 26, 2015
Does INH Affect the outcome of a PPD Test?
Two months ago I tested positive for Latient TB at 16mm. I had no indications of being exposed at all but I am in the military and we test for it no matter what every year. They placed me on INH. I am experiencing dizziness when getting up, I am tired all the time and very easily irritated. I went back in and had another test done. This time it came back negative. The nurse told me this was because I am on INH at the time and she said that another test should have never been done? Is this true? I thought that INH would have no affect on the results.
Up to one third of persons who have had recent TB exposure and a positive TB skin test will revert their skin test to negative if treated promptly with INH. Many of these skin test reversions will not last...ie the negative test again becomes positive at a later time. The reason for these changes is not clear.
So, it is possible that the negative skin test result is related to treatment with isoniazid.
Catherine A Curley, MD, MS
Assistant Professor of Medicine
School of Medicine
Case Western Reserve University