Specimen Submission Guidelines for Pathologic Evaluation of Influenza Virus Infections

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Viral antigens and nucleic acid may be focal or sparsely distributed in patients with influenza, and are most frequently detected in respiratory epithelium of large airways. Larger airways (particularly primary and segmental bronchi) have the highest yield for detection of influenza viruses by immunohistochemistry (IHC) staining and molecular testing (PCR). Collection of the appropriate tissues ensures the best chance of detecting the virus by IHC or PCR. Performance of specific immunohistochemical, molecular, or other assays will be determined using clinical and epidemiologic information provided by the submitter and the histopathologic features identified in the submitted tissue specimens.

Collection of Tissue Specimens

The preferred specimens would be a minimum of 8 blocks and fixed tissue specimens representing samples from the following pulmonary sites in addition to specimens from other organs showing pathology. Formalin-fixed, paraffin-embedded blocks made from BAL can also be submitted.  The recommended pulmonary sites include:

  1. Central (hilar) lung with segmental bronchi, right and left primary bronchi
  2. Trachea (proximal and distal)
  3. Representative pulmonary parenchyma from right and left lung

For patients with suspected myocarditis, encephalitis, or rhabdomyolysis, specimens should include myocardium (right and left ventricle), CNS (cerebral cortex, basal ganglia, pons, medulla, and cerebellum), and skeletal muscle, respectively.

Specimens should be included from any other organ showing significant gross or microscopic pathology.

Submission of Specimens

Paraffin-embedded tissue blocks

In general, this is the preferred specimen and is especially important to submit in cases where tissues have been in formalin for a significant time. Prolonged fixation (>2 weeks) may interfere with some immunohistochemical and molecular diagnostic assays.

Wet tissue

If available, we highly recommend that unprocessed tissues in 10% neutral buffered formalin be submitted in addition to paraffin blocks. The volume of formalin used to fix tissues should be 10x the volume of tissue. Place tissue collected according to the dimensions provided above in 10% buffered formalin for three days (72 hours) for biopsies, and a week for thinly-sliced autopsy tissues. After fixation, if not paraffin-embedded, tissues SHOULD be transferred to 70% ethanol for long term storage and for shipping.

Electron Microscopy (EM) specimens

Samples fixed in glutaraldehyde and held in phosphate buffer. Sample containers are filled to the top with phosphate buffer and sent on wet ice.  Do not freeze.  Epoxy-embedded tissues are also accepted.

Please refer to our General Guidelines for Submitting Pathology Specimens.