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Histology - General Information

General Guidelines for histology submissions

Please provide as many clinical details as possible on your submission form.  A picture tells a thousand words: if you can, send photos - digital photos can be emailed to your pathologist.  Alternatively, you can provide images on a CD or upload them to a file-sharing site.  Pathologists will view these photos with the case slides and history provided on the submission form.

Tissues in formalin must be submitted in sealed plastic bags separated from any specimens for cytology. Formalin fumes cause artefact in the cytology specimens that reduces staining quality to a level that is often insufficient for diagnosis. Specimens should be shipped in leak-proof containers and with appropriate labelling.

Please be very careful not to put fresh tissue into narrow-necked containers. Fixed tissue becomes firm and warps in fixation; whilst you may have been able to squeeze it into a container, it can then conform to the shape of the container (losing its anatomic orientation) and may be impossible for us to retrieve it without cutting it or breaking the container.

The rule of thumb for tissue:formalin volume is 1:10. Formalin penetrates tissue slowly and might only penetrate 0.5 cm into a tissue block. Tissues placed in formalin must therefore be kept as thin as possible; slices of only 1 cm in each dimension is optimal.

The standard all-purpose fixative is 10% buffered formalin. This is made by adding 9 volumes of water to one volume of commercial formalin (available as 40% formaldehyde) and buffering it to pH 7.  Formalin that is incorrectly buffered has a deleterious affect on nuclear staining and causes yellow-brown deposits to form in the tissues (acid haematin).  Neutralised (buffered) formalin (NBF) is easily made by adding 5 g of limestone chips to every 2 L of 10% solution.

Formalin vapour is an irritant and potentially carcinogenic. It may cause dermatitis in susceptible individuals. Formalin should only be handled in well-ventilated areas and care taken at all times to avoid direct contact with the skin and mucous membranes. PPE including gloves, gown and safety glasses are strongly recommended.

Formalin fixation makes most pathogens inert once complete, with the known exception of prion proteins.

Specimen:

Tissue

Container:

Screw-top plastic pots, and larger sealable buckets containing 10% formalin. The ratio of formalin to tissue should be 10:1.

Shipping Requirements:

All samples must be shipped in leak-proof, sealed containers with appropriate labelling (i.e. name, date, specimen/site).  Sample containers and shipping materials can be ordered from Gribbles Veterinary Pathology.