AW: [Histonet] overfixation with formalin _ methylene glycol

[Gudrun Lang]

Tony, thank you for your response.

Do you know about any research on the effect of methylene glycol on native
tissue?
I made a Google search and wasn't really successful.

It's a low concentrated di-ol, only present in aequous solution. Because
small and hydrophilic it will penetrate tissue fast. It's action on
cellmembrane-lipids??
In formalin about 99% is methylene glycol and therefore gives a w/w % about
59%_ instead of 36% formaldehyde. (Perhaps comparible with 50% ethanol?)

Hmm, questions...

Gudrun

-----Ursprüngliche Nachricht-----
Von: Tony Henwood (SCHN) [mailto:tony.henwood <@t> health.nsw.gov.au] 
Gesendet: Montag, 05. November 2012 00:21
An: 'gu.lang <@t> gmx.at'; histonet <@t> lists.utsouthwestern.edu
Betreff: RE: [Histonet] overfixation with formalin

Hi Gudrun,
Over-fixation is likely to decrease IPX staining at the edges (since it
would require harsher antigen retrieval).

I agree with you. Many of the edge affects with IPX and several special
stains (including H&E and Modified Orcein (for HBSAg etc) on Liver bx) are
more probably dur to air-drying of the biopsies prior to fixation (similar
seen on cautery specimens) or compression due to the needle as you
suggested.

Regards
Tony Henwood JP, MSc, BAppSc, GradDipSysAnalys, CT(ASC), FFSc(RCPA)
Laboratory Manager & Senior Scientist
Tel: 612 9845 3306
Fax: 612 9845 3318
the children's hospital at westmead
Cnr Hawkesbury Road and Hainsworth Street, Westmead Locked Bag 4001,
Westmead NSW 2145, AUSTRALIA 

-----Original Message-----
From: histonet-bounces <@t> lists.utsouthwestern.edu
[mailto:histonet-bounces <@t> lists.utsouthwestern.edu] On Behalf Of Gudrun Lang
Sent: Sunday, 4 November 2012 5:41 AM
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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