The formaldehyde fixation rate of tissue is determined from a combination of
the penetration rate, which is governed by diffusibilty,
the maximal covalent formaldehyde binding time, which is governed by the
formaldehyde 'clock' reaction, and the slow subsequent cross-linking which
This slow cross-linking is thought to be almost complete by 7 days post
formaldehyde binding time, but can continue over longer time periods.
What your investigator has found, is probably the published data related to
the maximal covalent formaldehyde binding time, i.e. 24 hours at room
as determined by Fox et al (reference #1). This study was essentially
independent of diffusibilty, i.e. negligible penetration time, since 16
micrometer thick sections of rat kidney were the substrate.
However, this study does not take into account subsequent further
A study by Helander (reference #2) determined the maximal covalent
formaldehyde binding time as 25 hours.
This was performed on 4 mm thick slices of rabbit liver, so diffusibility
has to be taken into account.
In addition, this study also partially looked at subsequent further
cross-linking in relationship to reversibility.
A later study by Helander (reference #3) compared the maximal covalent
formaldehyde binding time between kidney and brain tissues.
This was stated to be 50 hours however, the tissues thickness was increased
to 8 mm and so the diffusibilty effect has to be taken into account even
Fox CH., et.al. Formaldehyde fixation. J Histochem. Cytochem. 1985; 33,
Helander, KG. Kinetic studies of formaldehyde binding in tissue.
Biotechnique and Histochemistry. 1994; 69, 177 -179
Helander, K.G. Formaldehyde binding in Brain and Kidney: A kinetic study of
The Journal of Histotechnology. 1999; 22(4), 317-318.
----- Original Message -----
Sent: Tuesday, May 27, 2008 4:45 PM
Subject: [Histonet] Rate of formalin penetration in human brain sections
> One of our investigators is interested in the approximate rate of fixation
> of human brain tissue, independent of any formaldehyde diffusion effects.
> In other words, in a very small or very thin piece of human brain tissue,
> what is the fixation rate? He found published data for rat kidney, but
> would like to try to at least determine if the fixation rate should be
> higher or lower in human brain tissue. He is looking for data for room
> temperature, but any information would be greatly appreciated.
> Karen M Skish, MS, PA(ASCP)MT
> Pathologists' Assistant & Manager, Neuropathology Lab
> Rush Alzheimer's Disease Center
> Cohn Research Building, Lab 441
> 1735 West Harrison Street
> Chicago IL 60612
> Histonet mailing list
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