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Dr. Andrew Rynne
MD
Dr. Andrew Rynne

Family Physician

Exp 50 years

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Positive PPD result. Started with isoniazid. Suggest?

hi,im cheryl, i had my ppd test result 9mm and the nurse said it was positive,so they required me to have a blood test ,it turns out to be positive,so they asked me to have an x-ray .it turns out to be negative,but anyway i started to take isoniazid ,the dr. recommends it.after 5months of taking those pills ,the clinic called that i needed to have a bloodtest again because they might get the wrong result during those days when i got tested,we were 30 patients,some turn out to be still positive while others including me turns out to be negative.my question is that.does the second result turns to be negative because i was almost finished my 6months medication?or i was really negative from the very beginning.also i heard that positive ppd should be 10-12mm.but in my case ive got only 9mm but the nurse who measure it says its positive?
Mon, 4 Mar 2013
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General & Family Physician 's  Response
Hello Charlyn,

Thanks for posting on HCM,

Positive mantous test or PPD does not directly mean that you have an active TB infection. It could mean that you were ones exposed to TB but did not develop the diseases. Normally most immunocompetent people are PPD positive especially in high TB endemic regions. They are also false positive, true positive, false positive and true negative test results. These are determined by the size of the PPD and in your case, you probably had a false positive result (which signifies you are negative).
More over, the decision to place you on antiTB drug ( like isoniazid) should have been complemented with some clinical signs like presence of a pulmonary infection, lymphadenitis, POTs diseases and other signs that they might be a chronic infection that requires TB remedy. If you were not manifesting any signs of active TB (like night sweats, intermittent fever especially at night, signs of infection etc) then the decision to place on isoniazid based on positive PPD is wrongly justified.
Well after completing the treatment of TB, PPD could still come positive but active TB infection has been eradicated, therefore we still come to the point that taking isoniazid and evaluating directly with PPD is not properly justified. The only direct test is determining the presence of acid-fast-bacilli (AFB) myobacterium in either sputum, biopsy of a mass or lymph node etc.
I sincerely wish you the best
Dr Nsah
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Positive PPD result. Started with isoniazid. Suggest?

Hello Charlyn, Thanks for posting on HCM, Positive mantous test or PPD does not directly mean that you have an active TB infection. It could mean that you were ones exposed to TB but did not develop the diseases. Normally most immunocompetent people are PPD positive especially in high TB endemic regions. They are also false positive, true positive, false positive and true negative test results. These are determined by the size of the PPD and in your case, you probably had a false positive result (which signifies you are negative). More over, the decision to place you on antiTB drug ( like isoniazid) should have been complemented with some clinical signs like presence of a pulmonary infection, lymphadenitis, POTs diseases and other signs that they might be a chronic infection that requires TB remedy. If you were not manifesting any signs of active TB (like night sweats, intermittent fever especially at night, signs of infection etc) then the decision to place on isoniazid based on positive PPD is wrongly justified. Well after completing the treatment of TB, PPD could still come positive but active TB infection has been eradicated, therefore we still come to the point that taking isoniazid and evaluating directly with PPD is not properly justified. The only direct test is determining the presence of acid-fast-bacilli (AFB) myobacterium in either sputum, biopsy of a mass or lymph node etc. I sincerely wish you the best Dr Nsah