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Challenges in Ordering and Interpreting Pharmacogenomic Tests in Clinical Practice


More than 160 US Food and Drug Administration–approved medications have information in their labeling regarding genetic mutations known to be associated with efficacy or safety.1 Not surprisingly, pharmacogenomics is increasingly incorporated into clinical practice in an effort to optimize prescribing to improve treatment outcomes.2345 Clinical implementation of pharmacogenomics has been facilitated by efforts to standardize pharmacogenomic-related terminology and by the development of clinical practice guidelines.6789

Despite enthusiasm to improve patient care by utilizing pharmacogenomic knowledge, barriers still exist. Although most clinicians believe that pharmacogenomics will be important in their future practice, their comfort level with pharmacogenomics is low.1011 In addition to determining which gene(s) to test, providers must identify and select from a multitude of laboratories that provide a particular test. Then clinicians must interpret the test results and make appropriate treatment decisions based on the findings.

To better understand the difficulty clinicians encounter when selecting a laboratory for pharmacogenomic testing and interpreting the testing results, we assessed the availability of information on pharmacogenomic testing options in the United States and the variability in testing and result reporting among testing laboratories.


The Genetic Testing Registry (GTR)12 and GeneTests13 websites were searched in October 2015 to identify laboratories in the United States performing pharmacogenomic testing of CYP2D6 and/or CYP2C19 as a single gene test or part of a gene panel. CYP2D6 and CYP2C19 were selected as representative pharmacogenomic genes because they have more than 1 clinically actionable variant allele, guidelines have been developed with recommendations on how to use the test results in clinical practice, and medications affected by variants in these genes are frequently prescribed by a broad spectrum of providers. In addition to identifying laboratories offering tests for these 2 genes, the availability of details related to testing was assessed. The websites were searched for information on the specific alleles queried/reported, whether deletion/duplication analysis was included (for CYP2D6), how the data were reported (ie, genotype/“star” allele vs phenotype), and turnaround time. If a laboratory was listed on these websites but pharmacogenomic testing information was not readily available online, a survey was sent to the laboratory to attempt to gather this information; telephone calls were made to laboratories that did not respond.

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-Ann M. Moyer, MD, PhD, Carolyn R. Rohrer Vitek, MS, Jyothsna Giri, MD, Pedro J. Caraballo, MD

This article originally appeared in the December 2017 issue of The American Journal of Medicine.

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