Question:

If a person is HIV positive and they have symptoms for active tuberculosis but the tuberculosis skin test is negative do experts recommend beginning antituberculosis treatment until results other tests (sputum smears and cultures) come back with a more definitive diagnosis? If so is there a CD 4+ count that guides this, e.g., if the CD 4+ is below 200 or patient has AIDS?

Answer provided by:

Daniel Lee, M. D.
Assistant Clinical Professor of Medicine
UCSD Medical Center
Owen Clinic

In regards to your question, it is not entirely clear if one should start TB therapy in an HIV positive patient if they have symptoms suggestive of TB with a negative TB skin test. Skin tests in HIV patients are not diagnostic for active TB. It only indicates if one has been exposed to TB. Even then, HIV patients can often have TB with a negative skin test (due to the patient's poor immune system its inability to mount a positive response on the skin test). The decision to start a patient on TB medications is dependent on the clinician's suspicion of TB. However, this is a much debated issue and different clinicians will likely give you a different opinion. For example, if someone has a cough, fever, and weight loss, I may not start someone on TB therapy as many other infections can cause the same symptoms. However, if this person also had a report of a known TB exposure or had a chest x-ray showing a cavitary lung lesion, my suspicion would be higher and I would lean towards treating the patient. Nowadays, some of the TB tests (i.e. sputum AFB smears and MTD [Mycobacterium Tuberculosis Direct] probes) return within a day or two (compared to AFB cultures which can take up to 6-8 weeks) such that we usually can keep patients in respiratory isolation and wait for these results before starting TB medications. In regards to a CD4 cutoff, I am not aware that there is one that guides whether or not to start therapy before or after obtaining a more definitive diagnosis. Of note, TB is always something we should consider regardless of the CD4 count.

Thanks for your question.

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