Fixation on Histology

All About Iron: The Colloidal Iron Stain and Prussian Blue Reaction


Colloidal Iron StainIn a recent post, we talked about the Alcian Blue and Mucicarmine stains, which are both used for mucins, Alcian Blue for epithelial and connective tissue, and Mucicarmine for just epithelial tissue, but there is another mucin stain we have not talked about yet, and that is Colloidal Iron. Colloidal Iron is also used for acid mucins, but it can detect very small quantities, which is why it is sometimes used over Alcian Blue. In addition to mucins, Colloidal Iron is used in chromophobe renal cell carcinoma, Cryptococcus neoformans, a fungal infection that causes symptoms primarily in immunocompromised patients, and mast cell granules.

In this staining procedure, the positively charged iron ions in the colloidal iron solution bind with the negatively charged mucins. A potassium ferrocyanide hydrochloric acid solution is used, which reacts with the iron ions to form blue deposits. This histochemical reaction is actually known as Prussian Blue, or Perl’s reaction, which you might be familiar with as another staining method, but it is really a chemical reaction in which the iron ions and potassium ferrocyanide hydrochloric acid react to create a blue byproduct, ferric ferrocyanide. In the case of the Colloidal Iron stain, the reaction is occurring because iron was introduced to bind with the mucins, so the mucins could be demonstrated, but the reaction can also be used to detect iron that is naturally occurring in the patient.

In that case, HCL is used to release the iron in hemosiderin, an iron storage complex found within cells. Once the iron is released, the ferric ions react with potassium ferrocyanide to create Prussian blue. This is often used for identifying iron deficiency in cases of anemia, or alternatively too much iron, in cases of hemochromatosis. It can be also used in cases of Asbestos exposure, which causes ferruginous bodies, fibers coated with iron-rich material.

Learn more about iron stains in NSH’s HT Prep Course, which covers histology basics, such as staining, microtomy, processing, and fixation, to prepare you for the HT exam.