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The page below is a sample from the LabCE course Immunohistochemistry (IHC) Basics in Histology. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Blocking Endogenous Peroxidase Activity

Endogenous peroxidase is found in some normal and neoplastic tissues, as well as RBCs and leucocytes. Blocking endogenous peroxidase is a necessary step in methods that use a peroxidase-based detection systems to prevent false-positive staining reactions.
The most common method is a 5 to 10 minute incubation with 0.3% to 3.0% hydrogen peroxide (H2O2) in phosphate buffered saline (PBS), methanol, or distilled water at room temperature. This procedure may be performed before the application of the primary antibody or after the link antibody incubation. Using the methanol based H2O2 solution is harsher than the other mixtures. This is commonly used with blood smears, bloody/inflamed, and/or vascular tissues. There are pre-mixed solutions available that not only block endogenous peroxidase activity but some of the other unwanted enzymatic activity as well.