ODM2 Variable Name Controlled Vocabulary ODM2 Working Group A vocabulary for describing the name of Variables. Cytochrome P450, family 1, subfamily A, polypeptide 1, delta cycle threshold Delta cycle threshold for Cytochrome P450, family 1, subfamily A, polypeptide 1 (cyp1a1). Cycle threshold is the PCR cycle number at which the fluorescent signal of the gene being amplified crosses the set threshold. Delta cycle threshold for cyp1a1 is the difference between the cycle threshold (Ct) of cyp1a1 gene expression and the cycle threshold (Ct) for the gene expression of the reference gene (e.g., beta-actin). Originally from the CUAHSI HIS VariableNameCV. See: http://his.cuahsi.org/mastercvreg/edit_cv11.aspx?tbl=VariableNameCV.