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Q&A column, 5/18

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Editor: Frederick L. Kiechle, MD, PhD

Submit your pathology-related question for reply by appropriate medical consultants. CAP TODAY will make every effort to answer all relevant questions. However, those questions that are not of general interest may not receive a reply. For your question to be considered, you must include your name and address; this information will be omitted if your question is published in CAP TODAY.

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Q. Our immunohistochemistry laboratory is moving to a new building across the street. We are not getting new equipment, just moving the machines to the new building. Do we need to perform a full revalidation of all our antibodies?

A. Relocation of an instrument requires system verification rather than full analytical validation or revalidation, such as would be done with a new test, or antibody/antibody clone in the case of immunohistochemistry. Pertinent CAP checklist items include ANP.22750, ANP.22780, COM.30550, and COM.40000; they address equipment performance verification (does the equipment/instrument function properly) and test method performance specifications (does the antibody perform as previously validated on the equipment).

Laboratories should follow the instrument manufacturer’s guidelines and instructions throughout all steps of the relocation, paying special attention to any environmental conditions that might affect system operation. While the number of positive and negative cases to test has been established for antibody validation1—e.g. when changes are made to antibody dilution, antibody vendor (same clone), and incubation and/or retrieval times (same method)—details on verification for laboratory relocation are left to the discretion of the laboratory director. Factors to consider in that decision reflect the breadth, volume, and complexity of any given immunohistochemistry laboratory (see CAP checklist item ANP.22780). A verification plan should be written and approved before relocation.

The literature cites best practices for verification after laboratory relocation; they include testing a sufficient number (depending on immunohistochemical test menu and volume) of predictive and nonpredictive antibodies. In addition, when the laboratory director determines the antibodies to be tested for verification, different cellular antibody localization (nuclear, membranous, cytoplasmic, etc.) and variation in pretreatment and detection systems (heat-induced epitope retrieval versus others, etc.) should be considered. As with other verifications, cases expected to stain positively and negatively should be included. Predictive markers may deserve special consideration.

Stained slides of the tested antibodies should be compared from before and after the relocation and confirmed to show equivalent performance before clinical patient testing is resumed at the new site. If there are any problems or issues identified with the limited antibody testing for verification, the laboratory director must determine if full validation is needed for any or all antibodies. As with all verifications and validations, complete documentation should be performed and maintained in accordance with all regulatory and accreditation requirements.

  1. Fitzgibbons PL, Bradley LA, Fatheree LA, et al. Principles of analytic validation of immunohistochemical assays: guideline from the College of American Pathologists Pathology and Laboratory Quality Center. Arch Pathol Lab Med. 2014;138(11):1432–1443.

Kristin Clare Jensen, MD
Associate Professor of Pathology, Veterans Affairs Palo Alto Health Care System and Stanford University School of Medicine, Palo Alto, Calif.
Member, CAP Immunohistochemistry Committee

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Q. What is the value of CYP2D6 in opioid prescribing?

A. The best studied pharmacogene related to pharmacokinetics of opioids is CYP2D6, which codes for a major drug-metabolizing enzyme of the same name. Dosing guidelines from several organizations and drug-labeling content that reflect the relationship of predicted CYP2D6 phenotype to opioid selection can be found at www.pharmgkb.org. It is noteworthy that published guidelines do not recommend widespread testing, nor do they recommend the content of testing for this very complex gene. Instead, the guidelines help apply what is known to a situation, with caution. I am not aware of any pharmacoeconomic studies demonstrating the benefit of CYP2D6 testing for opioids specifically. The actual value of testing will likely depend on the patient population. For example, people with preexisting apnea or other respiratory concerns will be at increased risk of opioid toxicity, as will patients taking other medications that may augment the toxic effects of opioids (e.g. benzodiazepines). These patients may benefit from pharmacogenetic testing to evaluate their overall (genetic and nongenetic) risk of toxicity. Also, patients with a personal history or family history of opioid toxicity may benefit from knowing their predicted CYP2D6 phenotype.

The approach to management is typically to avoid CYP2D6-related opioids for patients who carry genetic variants and are predicted to exhibit either poor or ultra-rapid metabolism rather than dose optimization. While this strategy avoids the CYP2D6-related concerns, it does not mitigate risk of or guide selection of alternative therapeutic options.1 A recently published “shortlist” of 10 pharmacogenes that are recommended for implementation in pain management includes CYP2D6 as well as seven other pharmacogenes related to pharmacokinetic processes that affect select opioids: ABCB1, ABCC3, COMT, CYP3A4, CYP3A5, SLC22A1, and UGT2B7.2

  1. Crews KR, Gaedigk A, Dunnenberger HM, et al.; Clinical Pharmacogenetics Implementation Consortium. Clinical Pharmacogenetics Implementation Consortium guidelines for cytochrome P450 2D6 genotype and codeine therapy: 2014 update. Clin Pharmacol Ther. 2014;95(4):376–382.
  2. Matic M, de Wildt SN, Tibboel D, van Schaik RHN. Analgesia and opioids: a pharmacogenetics shortlist for implementation in clinical practice. Clin Chem. 2017;63(7):1204–1213.

Gwendolyn A. McMillin, PhD, D(ABCC), Medical Director, Toxicology and Pharmacogenetics, ARUP Laboratories
Professor of Pathology, University of Utah School of Medicine, Salt Lake City
Former member, CAP Toxicology, Resource Committee

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Dr. Kiechle is a consultant, clinical pathology, Cooper City, Fla. Use the reader service card to submit your inquiries, or address them to Sherrie Rice, CAP TODAY, 325 Wau­ke­gan Road, Northfield, IL 60093; srice@cap.org. Those questions that are of general interest will be answered.

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