I would first look at the local coverage determination for the Medicare carrier you are billing and look for similar policies for Medicaid and Private payers. As seen below for example WPS Medicare J5 has requirements on who can perform this service. This is for psychological testing. Wouldn't a psych eval be a referral to someone in that field.
https://www.cms.gov/medicare-coverage-database/details/lcd-details.aspx?LCDId=34646
Psychological Tests
A psychological test is an instrument designed to measure unobserved constructs, also known as latent variables. Psychological tests are typically, but not necessarily, a series of tasks or problems that the respondent has to solve. Psychological tests can strongly resemble questionnaires, which are also designed to measure unobserved constructs, but differ in that psychological tests ask for a respondent's maximum performance whereas a questionnaire asks for the respondent's typical performance. A useful psychological test must be both valid (i.e., there is evidence to support the specified interpretation of the test results) and reliable (i.e., internally consistent or give consistent results over time, across raters, etc.).
Psychological Assessment
Psychological assessment is similar to psychological testing but usually involves a more comprehensive assessment of the individual. Psychological assessment is a process that involves the integration of information from multiple sources, such as tests of normal and abnormal personality, tests of ability or intelligence, tests of interests or attitudes, as well as information from personal interviews. Collateral information is also collected about personal, occupational, or medical history, such as from records or from interviews with parents, spouses, teachers, or previous therapists or physicians. A psychological test is one of the sources of data used within the process of assessment; usually more than one test is used. Many psychologists do some level of assessment when providing services to clients or patients, and may use for example, simple check lists to assess some traits or symptoms. Psychological assessment is a complex, detailed, in-depth process. Typical types of focus for psychological assessment provide a diagnosis for treatment settings; assess a particular area of functioning or disability often for school settings; help select type of treatment or assess treatment outcomes; help courts decide issues such as child custody or competency to stand trial; or to help assess job applicants or employees and provide career development counseling or training.
Indications and Limitations of Coverage and/or Medical Necessity
Psychological testing
CPT codes 96101, 96102, 96103, 96105, 96111
Psychological tests are used to assess a variety of mental abilities and attributes, including Central Nervous System (CNS) Assessments such as neuro-cognitive, mental status, achievement and ability, personality, and neurological functioning.
Psychological testing requires a clinically trained examiner. All psychological tests should be administered, scored, and interpreted by a trained professional such as a clinical psychologist, psychologist, advanced nurse practitioner with education in this area or a physician assistant who works with a psychiatrist with expertise in the appropriate area. The purpose of psychological testing includes the following:
1. To assist with diagnosis and management following clinical evaluation when a mental illness or psychological abnormality is suspected.
2. To provide a differential diagnosis from a range of neurological/psychological disorders that present with similar constellations of symptoms, e.g., differentiation between pseudodementia and depression.
3. To determine the clinical and functional significance of a brain abnormality.
4. To delineate the specific cognitive basis of functional complaints.