Stains - Immunohistochemistry basics

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Immunohistochemistry basics

Reviewer: Nat Pernick, M.D., PathologyOutlines.com, Inc. (see Reviewers page)
Revised: 20 April 2011, last major update April 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.

General
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● Immunohistochemistry (IHC) is a tool for surgical pathology and research
● Diagnosis should be based on H&E morphology, with confirmation by immunohistochemistry or molecular testing; it is dangerous to use immunohistochemistry alone to make the diagnosis
● A stain / result is not just positive or negative; focus on the types of cells that are immunoreactive and determine if they are tumor cells, inflammatory cells, normal cells or stromal cells; comparing the results to an H&E stained section or a negative control of the same block may be helpful (Am J Surg Pathol 2007;31:1627)
● After you identify the type of cell staining, it is helpful to note the percentage of these cells staining, the intensity of staining (weak, 1+, 2+, 3+, 4+) and the pattern of staining (membranous, cytoplasmic, nuclear, dot-like)
● The pattern of immunoreactivity should follow the anatomic distribution of the antigen before it is called positive / immunoreactive

Common errors
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● Not using a positive or negative control; they are helpful in interpreting the staining pattern, particularly if it is heavy or weak
● Other sources of error are ectopic antigen expression, cross reactions, less specificity than thought, or rarely use of the wrong antibody

Other
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● Antibodies are often useful beyond their recommended expiration dates
● Combining results from different studies may be hazardous, as studies may use different antibodies and different standards of interpretation
● Recommended to interpret immunohistochemical stains in small needle core biopsy specimens based on the area with the greatest immunoreactivity (Am J Clin Pathol 2007;127:273)

End of Stains > Immunohistochemistry basics

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