Congo blue: a rapid stain for elastic fibres.

7Edberg SC, Bottonbley CJ and Gam K. Use of sodium polyanethol sulfonate to selectively inhibit aminoglycoside and polymyxin antibiotics in a rapid blood level antibiotic assay. There are numerous empirical methods for staining elastic fibres.' Most require relatively lengthy procedures which involve overnight incubation, and are therefore not adapted to simultaneous evaluation with the corresponding haematoxylin and eosin-stained sections. Congo red, a dye which was initially used in commercial colouring of cotton fabrics, is often employed for the diagnosis of amyloid in human tissue.23 Most batches of Congo red, even when used in the standardised saturated salt conditions described by Puchtler et al4 also stain elastic fibres. Such elastic staining can, of course, be a disadvantage when identification of amyloid is desired. Although the anisotropic and dichroic characteristics of amyloid usually distinguish it from elastic fibres, the inexperienced histopathologist may find the distinction difficult. This problem may be accentuated in the dermis, where the recent demonstration of the P component of amyloid in elastic fibres5 could well add to the confusion. The Congo staining method which we describe is a modification of that of Highman.3 It demonstrates elastic fibres clearly and distinguishes them sharply from amyloid. Material and methods The tissues were fixed in unbuffered fresh formol saline. They were processed via xylene for paraffin embedding in the routine manner. Paraffin sections (5 gm) were taken to water. The sections were stained with 0-5% (wt/vol) Congo red in 50% alcohol according to the method of Highman3 for 10 min. Thereafter the sections were rinsed in distilled water. Instead of the exposure to alkaline ethanol, appropriate for Highman's Congo red procedure, the sections are then rinsed for about 10 s in 1 % hydrochloric acid in 70% ethanol. With this treatment the sections become blue to the naked eye.