Mo. Rev. Stat. §376.1363(5)

(5) A written notification of an adverse determination shall include the principal reason or reasons for the determination, including the clinical rationale, and the instructions for initiating an appeal or reconsideration of the determination. A health carrier shall provide the clinical rationale in writing for an adverse determination, including the clinical review criteria used to make that determination, to the health care provider and to any party who received notice of the adverse determination.