Specimens should be fixed for approximately 6 to 72 hours,5 preferably for a minimum of 8 hours especially for larger specimens. • “Overnight” fixation (i.e. 8-12 hours) is generally indicated for 10 mm thick slices of tissues. Fixation for 12-24 hours is considered optimal for most immunohistochemistry.

What happens during fixation?

Fixation consists of two steps: cessation of normal life functions in the tissue (killing) and stabilization of the structure of the tissue (preservation). The goal of fixation is to preserve structure as faithfully as possible compared to the living state.

What is the purpose of fixation?

Fixation – types of fixatives. The purpose of fixation is to preserve tissues permanently in as life-like a state as possible. Fixation should be carried out as soon as possible after removal of the tissues (in the case of surgical pathology) or soon after death (with autopsy) to prevent autolysis.