To any of you who are tempted to substitute the grocery store dye Rit
Scarlet #5 for Congo red, please consider the following:

Rit dyes are intended for use on fabrics.  The manufacturer blends several
dyes together (direct, disperse and acid dyes) to achieve a particular
shade.  In the textile dye trade, dyes are frequently made rather crudely,
and hence vary considerably from lot to lot.  Vendors such as CPC Specialty
Markets USA, which makes the Rit dyes, probably blends several to match
some internal standard for Scarlet #5.  If one red component is a bit more
yellow this lot than last, final hue of the mixture is adjusted by altering
the other components.  It is certainly possible that the same components
might not even be used from lot to lot.  Anyone who has worked with fabric
or yarn dye lots is well aware of the variations in color that are rampant
in this field.

There may even be changes in the composition of the mixture as fabric
fashion changes.  Slight differences in fabric composition or finishing do
occur from year to year.  In an attempt to keep a particular mixture
popular, its components may be altered to better suit the new fabric.

To those of you who find this a bit far fetched, the Biological Stain
Commission was formed and exists today in part because of these vagaries in
the supplies of our dyes.

Yes, buying Congo red (or Sirius red F3B) from a reputable vendor is more
costly than picking up a packet of fabric dye at the grocery store.  The
people who make Rit do not purify and test their dyes for biological use
(in fact, they would probably be appalled at the legal implications of you
using their product for such a purpose).  The Rit people do not have to
conform to the FDA's requirements for manufacturing and labeling.  They
also do not serve a market that is so small that the total yearly
consumption of the product (100 lbs) is about that which is sold for fabric
use in one good-sized grocery store.

Congo red is certified by the Biological Stain Commission.  The tests that
are conducted on every batch submitted to the Commission are described in
Conn's Biological Stains (9th edition, pages 575-576).  One test includes
staining for amyloid using Highman's procedure.  Vendors pay for that
independent certification service.  It is your assurance that the dye
really works for the purpose you intend for it.

Quality control, regulatory compliance and the economies of scale make that
bottle of Congo red about 4 times more expensive than the fabric dye.
Please remember that before you criticize vendors of biological dyes and
stains.  Also, please remember that most of you are using Congo red on
human specimens.  You could be the patient.


Amyloid is a difficult material to stain consistently.  Its "Congophilia"
varies with its age, and with its origins.  Equivocal cases are common
enough that missed diagnoses must occur with some frequency. How would you
like to be the patient who discovered that, because of a few cents'
difference in price, your mis-diagnosed slide was stained with a grocery
store fabric dye?  Has our healthcare system come down to that?

Is your laboratory willing to risk the legal implications of using a dye
designed for household purposes when stains manufactured for in vitro
diagnostic use, or dye powder certified for staining amyloid, are readily
available?

Dick


Richard W. Dapson, Ph.D.
ANATECH LTD.
1020 Harts Lake Road
Battle Creek, MI  49015
800-262-8324 or 616-964-6450
Fax 616-964-8084
E-mail anatech@net-link.net
http://www.net-link.net/anatech