Category: Special Stains

Trichrome stains are primarily used to identify 𝐜𝐨𝐥𝐥𝐚𝐠𝐞𝐧 (a structural protein), bone or 𝐟𝐢𝐛𝐫𝐢𝐧 (the protein that forms blood clots). In general, collagen and bone are highlighted blue-green, while fibrin is highlighted in red.

PAS stands for 𝐩𝐞𝐫𝐢𝐨𝐝𝐢𝐜 𝐚𝐜𝐢𝐝-𝐒𝐜𝐡𝐢𝐟𝐟, and is a very common special stain used in pathology. It actually stains several things, so can be used for a lot of different purposes!

Rhodanine is a stain for 𝐜𝐨𝐩𝐩𝐞𝐫. Copper, 𝐥𝐢𝐩𝐨𝐟𝐮𝐬𝐜𝐢𝐧 (a cell aging pigment) and 𝐡𝐞𝐦𝐨𝐬𝐢𝐝𝐞𝐫𝐢𝐧 (a blood breakdown product) all look very similar on H&E, so these special stains help pathologists distinguish between the brown granules.

Congo red is used to stain 𝐚𝐦𝐲𝐥𝐨𝐢𝐝, which is an abnormally folded protein that can accumulate in tissues. This protein takes up a lot of space in the tissue, potentially resulting in organ damage.

Prussian blue (or Perl’s stain) is used to highlight 𝐢𝐫𝐨𝐧. On H&E, there are several brown pigments that can look similar, so special stains are needed to distinguish them.

GMS stands for 𝐆𝐨𝐦𝐨𝐫𝐢’𝐬 𝐦𝐞𝐭𝐡𝐞𝐧𝐚𝐦𝐢𝐧𝐞 𝐬𝐢𝐥𝐯𝐞𝐫. This stain is primarily used to highlight 𝐟𝐮𝐧𝐠𝐢.

Acid-fast staining is a special technique used to identify certain types of bacteria that do not stain with Gram stain.

The Warthin-Starry stain highlights certain types of 𝐆𝐫𝐚𝐦-𝐧𝐞𝐠𝐚𝐭𝐢𝐯𝐞 bacteria (see last week’s post on Gram stains!) that don’t absorb Gram stain.

Gram stains are probably one of the most frequently requested special stains. This stain highlights 𝐛𝐚𝐜𝐭𝐞𝐫𝐢𝐚, which can be incredibly difficult to identify on our standard H&E stain!

Oil red O is a red dye that specifically highlights 𝐟𝐚𝐭𝐬, dying them a bright red colour. Most of our stains can be done on 𝐟𝐢𝐱𝐞𝐝 𝐭𝐢𝐬𝐬𝐮𝐞 (tissue preserved in formalin), but the fixation process actually removes all of the fat! So this stain must be done on fresh or frozen tissue.