A punch biopsy of a skin lesion is taken from a patient and the pathologist orders direct immunofluorescence testing. Which of the following mediums should be used for transport?

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For direct immunofluorescence on a skin biopsy, the tissue must retain antibody and complement deposits as they were in the patient, without any fixation that could mask the antigenic sites. Michel’s transport medium is designed to preserve both tissue morphology and the antigenicity of immunoreactants while keeping structural proteins unfixed, so the deposits can be detected accurately when the specimen is examined, typically on frozen sections.

Formalin and glutaraldehyde fixatives cross-link proteins and destroy the epitopes needed for fluorescent antibodies to bind, making immunofluorescence unreliable. Normal saline lacks any fixation or antigen-preserving properties, so it does not protect the antigenicity of immunoreactants during transport.