Formalin is a commonly used fixative for tissue samples that are being submitted for histopathology. Tissue samples submitted in formalin jars undergo special processing that allow for preservation of the cells and good staining. However, for cells that are on a slide, formalin can have significant effects, causing rapid cell fixation and disintegration, limiting stain uptake with the stains used for cytologic evaluation. This ultimately affects the pathologist’s ability to provide a diagnosis on any cytology or blood film specimens that have had formalin exposure. Even exposure to formalin fumes can rapidly deteriorate cells, so it is critical that formalin is kept far away from cytology and hematology samples.
When submitting tissue samples in formalin or handling formalin, please take the following precautions to avoid slide degradation.
- Promptly close all containers to limit release of formalin fumes
- Keep any cytology and hematology slides away from any areas where formalin is used and when preparing and storing histopathology samples
- Close the specimen container tightly, seal with Parafilm, and enclose in a sealed bag (such as a Ziploc-type bag)
- Submit any associated cytology or hematology slides securely enclosed in a labeled slide carrier, sealed in its own sample bag
Note that formalin fumes may still permeate through plastic, so it is always important to keep formalin specimens away from cytology and hematology slides, even during transport to the laboratory.
Formalin will not affect blood or fluids inside of closed blood tubes.
Containment of formalin is not only important for preservation of cytology and hematology specimens, but formalin is a carcinogen that is a risk to human health; therefore, limiting risk of container leakage and formalin fume exposure is important even when not submitting cytology and hematology slides. Always use all recommended PPE when handling formalin.