Diagnosis:
Quality Control
• Although quality control measures cannot eliminate false positives and negatives, positive and negative assay controls should be performed with every run.
• Positive controls, in this context, are tissues known to express the antigen being tested for, preferably near the limit of detection required of the assay.
• Negative controls include negative tissue controls—tissue known NOT to express the antigen—and negative antibody controls, replacing the antibody with a relevant antibody free reagent (preferably normal serum of source animal species of the primary antibody).
• Each tested tissue should receive one negative antibody control for each combination of primary antibody source and antigen retrieval method—although many labs use only the “most powerful” antigen retrieval method.
• These procedures, however, cannot control for preanalytical variables, such as delay before fixation, completeness of fixation, overfixation, and so on, and, therefore, false positive and negative results can still occur.
Taylor CR, Shi S-R, Barr NJ, Wu N: “Techniques of immunohistochemistry: principles, pitfalls, and standardization.”In: Dabbs DJ (ed): Diagnostic Immunohistochemistry. New York: Churchill Livingstone, 2002, pp 3-44.