[Histonet] More on uric acid

[Bryan Hewlett]

Mike,

The sign of birefringence, i.e. determination of the vibration direction or
Positive and negative birefringence, is used to distinguish between
pseudogout (pyrophosphate crystals) and gout (uric acid or urate crystals).
Both types of crystal are birefringent.
A first order red compensator or Lambda plate is introduced diagonally (45
degrees) between the crossed polarizer and analyzer. The compensator has the
vibration direction of the slow ray marked on its handle. If the long axis
of the crystal in the section is aligned parallel to the compensator's
vibration direction, by rotating the microscope stage, an interference
colour will be seen due to addition or subtraction of small phase
differences.
A blue colour indicates addition or positive birefringence = pyrophosphate
(pseudogout).
A yellow colour indicates subtraction or negative birefringence = uric acid
or urates (gout).
N.B.  Both types of crystal may be blackened by hexamine silver!

It is best to avoid H&E stained sections for this procedure since the
aqueous steps and the blueing alkali may remove urates.
Dewax the sections thoroughly, 10 min X 3 xylenes since wax is birefringent,
mount unstained sections in resin. If you must stain for location purposes
use an alcoholic nuclear stain (weak 0.01% Methylene blue in 80% alcohol
etc.).

Regards,

Bryan

----- Original Message -----
From: <MTitford <@t> aol.com>
To: <Histonet <@t> lists.utsouthwestern.edu>
Sent: Tuesday, January 06, 2004 11:48 AM
Subject: [Histonet] More on uric acid


> To clarify Peggy Wenk's comments, when you do the methenamine silver
procedure, it is like a GMS but WITHOUT the oxidation.
> Go straight from deionized into the heated silver solution, and monitor it
microscopically. A positive control is good to have!
>
> Our pathologists talk about positive and negative birefrigence of uric
acid when looking at the H&E section with polarizing microscopy, but I can
never get it straight in my mind!
>
> Mike Titford
> USA Pathology
> Mobile AL USA
>
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