[Histonet] overfixation with formalin

[Gudrun Lang]

Hi histonetters!

I'm just attending a histo-course, where the teacher told us his opinion
about overfixation.

For him overfixation takes place in any formaldehyde solution with a
concentration above 5%. This should cause the margin-artefact, that leads to
false-positive IHC at the margins of the tissue and to false-negative
results in the center. The higher concetrated fixative should harden and
shrink the surface, so it cant be penetrated any more by the fixative.

 

I told him about the publication of Cecil Fox, who saw shrinkage only in
solutions with formaldehyde concentration above 30% (I think) and said, that
the methanol-part is responsible for that.

I believe, that these margin-artefacts are due to drying at the time of
biopsy or an effect of the needle-shot itself. (But believing is no
evidence)

 

In our lab we use 8% formaldehyde as standard fixative, buffered with
low-molar phosphatebuffer. There are no complains from the doctors about
margins.

 

Please help me with the histonet-wisdom. What's your opinion? 

 

Bye

Gudrun Lang