MRCP UK EXAMINATIONS

Detailed explanation-1: -AFB smears are ideal to identify mycobacteria but it is important to remember they do not differentiate between NTM and MTB. Therefore a positive AFB smear can be NTM or MTB and another test (culture and DNA probe) is necessary to tell the difference. A negative smear does not exclude an active TB diagnosis.

Detailed explanation-2: -If your results on an AFB smear or culture were negative, you probably don’t have active TB. But it could also mean there weren’t enough bacteria in the sample for your health care provider to make a diagnosis.

Detailed explanation-3: -Negative smears do not exclude TB disease (Table 4.3). Many TB patients have negative AFB smears with a subsequent positive culture. Negative smears do not exclude TB disease. When acid-fast bacilli are seen in a smear, they are counted.

Detailed explanation-4: -A positive smear signifies a very large bacterial population in the lung lesions whereas several negative smears suggest a smaller bacterial load. Such smear-negative cases do not require the same intensity and duration of treatment as smear-positive cases.