(1) The Montana medicaid program does not cover and will not reimburse for services provided in institutions for mental diseases, except:
(a) services provided to medicaid recipients ages 18 through 21 and 65 or over in hospitals devoted to the provision of inpatient psychiatric hospital care for adults; or
(b) as provided in ARM 37.88.1401, 37.88.1402, 37.88.1405, 37.88.1406, 37.88.1410, 37.88.1411 and 37.88.1420 for medicaid recipients age 65 or over receiving nursing facility services in a nursing facility that the department has determined to be an institution for mental diseases under ARM 37.88.1402.
(2) For nursing facility services provided to medicaid recipients age 65 years or over in an institution for mental diseases, the Montana medicaid program will pay a provider:
(a) for each patient day, an interim per diem rate, as specified in (3) , minus the amount of the medicaid recipient's patient contribution; and
(b) additional reimbursement for separately billable items as provided in (4) .
(3) The final per diem payment rate for:
(a) the Montana state hospital is $335; and
(b) the Montana mental health nursing care center at Lewistown is $150 for high acuity patients and $100 for low acuity patients.
(4) Separately billable items are those items specified in ARM 37.40.330 and are reimbursable by medicaid according to the provisions of ARM 37.40.330.
(5) For hospital services provided to medicaid recipients age 18 through 21 and 65 or over, the Montana medicaid program will pay hospitals devoted to the provision of inpatient psychiatric hospital care to adults an all-inclusive per diem rate which includes the cost of physician and dental services as well as the cost of the services listed in ARM 37.86.2902(2) .