Quantification of the ratio of clozapine to-N-desmethylclozapine, also known as norclozapine, in blood plasma. Clozapine is an antipsychotic drug used to treat schizophrenia and N-desmethylclozapine is a a major active metabolite of clozapine. The trait is plasma clozapine-to-N-desmethylclozapine ratio measurement (EFO_0600040). Also known as: plasma clozapine-to-norclozapine ratio measurement.