Many different terms are used to describe allele function and assign clinical phenotype. For example, a genetic laboratory report might assign an individual carrying two non-functional TPMT alleles as either being “TPMT homozygous deficient” while another laboratory might use the term “TPMT no activity”. Also, these same laboratories might use different terminology to describe a similar phenotype for a different gene (e.g., an individual carrying two non-functional DPYD alleles might be described as “DPYD defective.”). This lack of standardization is often confusing to clinicians and patients as the actual phenotypes are the same (i.e. no function), but the terms describing the phenotypes are different and thus, might be interpreted differently. Moreover, the lack of standardization hinders the development of standardized approaches for reporting and sharing pharmacogenetic test results across laboratories and in electronic health records (EHRs). To maximize utility of pharmacogenetic test results and to fully implement CPIC guidelines, it is desirable to standardize these terms. Phenotype terms should also be easily interpreted by clinicians with basic pharmacogenetic training, and where possible, should be interchangeable across genes (e.g., the use of “TPMT deficient” and “DPYD deficient” to describe an individual carrying two non-functional alleles).