1. Health care services covered by insurance that are necessary to preserve and maintain the health of a member of a managed care plan. The medical service provided must be necessary, appropriate according to current standards of medical practice, provided in the most appropriate setting, and performed at the proper level of service. 2. Cal. Wel. & Inst. Code 14059.5 defines medical necessity when it is reasonable and necessary to protect life, to prevent significant illness or significant disability, or to alleviate severe pain. See also medical necessity and medically (or psychologically) necessary services .