What decides how a pathology specimen travels is whether it has gone into fixative. Tissue placed in 10% neutral buffered formalin is chemically stabilised and travels at room temperature; according to the CAP and NSH surgical pathology guide, fixatives work effectively at 22-25 °C in any case. Unfixed fresh tissue keeps degrading, so it goes to the laboratory immediately and, if it has to wait, is refrigerated until it is placed in formalin.
Before a specimen in formalin leaves, three points are checked:
- The formalin volume is 15-20 times the specimen volume and the tissue stays fully submerged; a large specimen squeezed into a small container degrades where it is exposed.
- The container is leak-proof. The closure is tested by turning the filled container upside down, because leaking formalin both dries out the specimen and endangers whoever carries it.
- The cold ischaemic time, the time between removing the tissue and placing it in formalin, is written on the request form together with the identity details.
Fixation has its own window: the same guide recommends at least 6 and at most 72 hours in formalin, and a 4 mm thick piece of tissue is fully fixed in about 24 hours. For a long route or a dispatch that runs into a weekend, check that the laboratory can process the specimen within that window.
