The invention teaches derivatives of mycophenolic alcohol and methods of preparing immunogens and other conjugates useful in immunoassays for quantitatively measuring concentrations of mycophenolic acid (MPA) and/or active metabolites of MPA in patient specimens. Antibodies produced from the disclosed immunogens capable of binding to MPA with cross-reactivity of no more than 5% with inactive metabolites and commonly co-prescribed drugs. Further, immunoassays for measuring the concentration of MPA using such antibodies are taught.