Positive AFB Sputum but Negative PPD Mantoux Test? How is this possible

Is it possible to have a positive acid fast bacilli sputum test and at the same time also have a negative mantoux ppd test?
Both of these test for TB...so would having a + AFB test automatically mean that you have TB? I had a pt today who was growing bacteria in the sputum samples but they had a ppd test done and it was negative. I don't get it! Wouldnt this mean that you have active TB?
I think it is possible to have a positive AFB and negative PPD because many things can be a factor such as immunosuppresion and all that, the person most likely has active TB and needs a chest x-ray for confirmation..

So a positive AFB test would be 100% that the person is infected with TB? Theres no way to have a positive cx and no evidence of TB right? Sorry for all the Q's I just find the diagnosis and tx of tb very difficult to understand sometimes. We didnt really go over it much even in community nursing class really...

ppd, if administered correctly, will always be positive if the patient has been exposed to tb. it can, however, be incorrectly administered or read.acid fast + from septum can be caused from any organism from the mycobacteria family. however it is usually tb.odds would favor the initial ppd test being read or administered incorrectly. look for horses, not zebras. mycobacteria in septum that isn't tb is a zebra.

There are several reasons for a false negative Mantoux test.Severely weakened immune system: AIDS with low CD4 T cell count, corticosteroid or chemotherapy drugs,Vaccination with a live virusImproper testing: Sometimes the PPD tuberculin may be injected too deeply below the surface of the skin. Recent TB infection: It usually takes eight to 10 weeks after you've been infected for your body to react to a skin test.Overwhelming TB disease.

Quote from RN2B123So a positive AFB test would be 100% that the person is infected with TB? Theres no way to have a positive cx and no evidence of TB right? Sorry for all the Q's I just find the diagnosis and tx of tb very difficult to understand sometimes. We didnt really go over it much even in community nursing class really...

Why bother administering a PPD if the sputum test was +?

Quote from roser13Why bother administering a PPD if the sputum test was +?

I don't mean to hi-jack the thread but I have a couple of questions which are primarily for the LTC nurses although not exclusive. Do you utilize the 2-step PPD testing on admission to reduce false negatives and have you seen the booster phenomenon? Is this done for everyone or just the patients determined to be more at risk with immune system compromises other than just age?The LTC can also include those in the prisons and other long term incarcerations.