Clinical exome sequencing is a genetic technology making the transition from a laboratory research tool to a routine clinical technique used to diagnose patients. Standards help make this transition by offering authoritative shortcuts for time-intensive tasks, but each shortcut means that something is lost during abstraction. In clinical exome sequencing, reliance on standards may obscure the match between a patient's phenotype and genotype. Based on three years of observations, I show how a clinical exome sequencing team decides when to trust standards and when to develop workarounds. I argue that the match between phenotype and genotype is circumscribed by the team's reliance on specific standards and that trusting in standards means trusting in experts' appropriate use of standards, generating a workflow of reflexive standardization.