The following specimens and/or diagnoses require fresh tissue for a complete workup:
- Muscle biopsy to rule out myopathy.
- Nerve biopsy to rule out neuropathy.
- Kidney biopsy to rule out nephropathy.
- Lymph node biopsy to rule out lymphoma.
- Tissue for culture of infectious organisms.
- Tissue for genetic analysis.
Except for the above, almost all specimens processed in the surgical pathology laboratory should be placed in a formalin fixative which preserves the tissue. Specimens which remain for longer than 24 hours without a fixative may undergo degradation which can prevent the pathologist from making a diagnosis. However, formalin fixative has certain properties that may prevent the use of ancillary testing on specimens. Formalin stops enzyme activity within tissues. This is good for preservation, but if the patient is being worked up for myopathy or neuropathy, formalin will prevent investigation of metabolic abnormalities. Kidney biopsies to rule out glomerulonephropathy require three different fixatives for electron microscopy, immunofluorescence microscopy, and light microscopy. Lymphomas are best classified using a combination of light microscopy and cell surface antigen analysis by flow cytometry which requires a fresh, unfixed tissue sample. Formalin fixation kills all microorganisms, so specimens for culture cannot be fixed. It is best to send the microbiologic specimen and requisition completely separate from the histology specimen and requisition because the laboratories are different and the sterility of the sample may not be optimal if sent to histology. Finally, formalin causes destruction of DNA sequences so DNA testing such as cytogenetics and PCR should be done on unfixed tissue. Genetic testing is useful for various leukemias, pediatric tumors (neuroblastoma, rhabdomyosarcoma), and congenital birth defects.
If the specimen falls into one of the special categories listed at the top of this page, the following instructions will help preserve the specimen. If a muscle, nerve, or lymph node biopsy is removed in one of the operating rooms at Renown Regional Medical Center, the histology laboratory should be called at extension 7753 and a pathologist will pick up the specimen. Ultrasound-guided kidney biopsies can be evaluated at the bedside to confirm the presence of renal tissue and then can be apportioned to the various fixatives.