AW: [Histonet] overfixation with formalin

[Rene J Buesa]

If methanol has reached a high concentration on the formalin solution it will act by itself both fixing (double fixation effect) and dehydrating.
René J.


________________________________
From: Gudrun Lang <gu.lang <@t> gmx.at>
To: "'Rittman, Barry R'" <Barry.R.Rittman <@t> uth.tmc.edu> 
Cc: Histonet <@t> lists.utsouthwestern.edu 
Sent: Sunday, November 4, 2012 3:13 AM
Subject: AW: [Histonet] overfixation with formalin

Thanks for your support.
Another theory about margin effect could be, that the methylenglycol in
formalin is the main reagens. Isn't it possible, that it acts like other
alcohols with dehydration at the surface (0,2-0,4 mm). But I think this
effect is too weak to inhibit the center to be fixed properly. I still
think, that it is too short fixation (no time for crosslinking) that causes
"bad" centers.
Gudrun

-----Ursprüngliche Nachricht-----
Von: histonet-bounces <@t> lists.utsouthwestern.edu
[mailto:histonet-bounces <@t> lists.utsouthwestern.edu] Im Auftrag von Rittman,
Barry R
Gesendet: Samstag, 03. November 2012 20:32
An: histonet <@t> lists.utsouthwestern.edu
Betreff: RE: [Histonet] overfixation with formalin

Gudrun
I  would thank him for his opinion and move on.
There has always been the unfortunate tendency to accept anything that is
published or presented formally as if it were gospel.
I am a lot more skeptical, give me proof.
Barry
________________________________________
From: histonet-bounces <@t> lists.utsouthwestern.edu
[histonet-bounces <@t> lists.utsouthwestern.edu] On Behalf Of Gudrun Lang
[gu.lang <@t> gmx.at]
Sent: Saturday, November 03, 2012 1:41 PM
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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