[Histonet] overfixation with formalin

[Edwards, Richard E.]

I have  seen far  more  damaged/unusable (apart from H <@t> E)   tissues through under-fixation than over-fixation.....................

-----Original Message-----
From: histonet-bounces <@t> lists.utsouthwestern.edu [mailto:histonet-bounces <@t> lists.utsouthwestern.edu] On Behalf Of Gudrun Lang
Sent: 03 November 2012 18:41
To: histonet <@t> lists.utsouthwestern.edu
Subject: [Histonet] overfixation with formalin

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

 

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