After performing a PPB technique, you look under the microscope and can't find any evidence of ferritin on your control slide and patient slides. What could be the probable cause?

• A. Forgot to add HCL to histochemical solution
• B. Potassium ferrocyanide was made up two months before use
• C. Tissue was fixed in Bouin's
• D. Counterstain obscured ferritin

Answer: (A)

The key concept is that the ferritin detection with the Prussian blue reaction requires an acid step to release iron from ferritin so it can react with the ferrocyanide to form the blue precipitate. Hydrochloric acid is used to liberate Fe3+ from ferritin; without this liberation, there’s no Fe3+ available to form Prussian blue, so no ferritin signal appears on any slide. If you forgot to add the acid, the staining would fail entirely for both control and patient slides, which matches the observed result. Other scenarios, like using old ferrocyanide, fixing in Bouin’s, or a counterstain obscuring color, could affect intensity or visibility but wouldn’t as reliably produce a complete absence of ferritin staining on all slides.