What should be done with a lymph node biopsy fixed in formalin submitted for AFB smear?

A lymph node biopsy fixed in formalin should be rejected for an AFB smear due to the nature of formalin and its effects on the specimen. Formalin is a fixative that preserves cellular structures but can significantly hinder the detection of acid-fast bacilli (AFB). The chemicals in formalin can disrupt the integrity of the mycobacterial cell wall, rendering AFB negative or causing false-negative results. Therefore, such a specimen is not suitable for the AFB smear methodology, which relies on the preservation of the mycobacteria's characteristics.

In contrast, if the biopsy had been collected and processed appropriately without fixation, it could be accepted and tested for AFB smear and culture. The preservation of viable bacteria is crucial for accurate microbiological diagnosis, particularly for slow-growing organisms like mycobacteria. Thus, the decision to reject the specimen fixed in formalin aligns with the requirements for effective diagnosis.