A claim by a beneficiary or supplier/assignee  must be  accompanied by the attending physician's prescription or documentation from the attending
            physician supporting the need for the equipment. The physician's prescription or other
            documentation should include the patient's diagnosis and prognosis, the reason the
            equipment is required, and the physician's estimate in months of the duration of the
            equipment's need. When prescribing oxygen, written documentation from the physician
            must be included, specifying the oxygen flow rate and concentration level and an estimate
            of the frequency and duration of oxygen use by the patient. Where any of the above
            information is lacking, the carrier will make reasonable inferences from the other
            information on the prescription or other documentation. For example, where the attending
            physician has prescribed an IPPB machine but has failed to indicate the physician's
            estimate of the period of medical necessity, the carrier could readily infer from
            a diagnosis of severe pulmonary emphysema that the equipment will be needed long enough
            to warrant purchase when the condition is stable, chronic, and non-life threatening.
            If the information cannot be inferred and is not obtainable from the carrier's files
            or from other readily available sources, the carrier will request the required information
            from the physician through written, personal or telephone contact.
         
         Where the information cannot be obtained from the above sources, the carrier will
            request the beneficiary or supplier/assignee to obtain from the attending physician
            a written statement containing this information.
         
         If, after obtaining the information, a question of medical necessity remains, the
            issue is resolved by the carrier's medical staff or other professional consultation.
            Where the evidence is insufficient to determine medical necessity, the carrier may
            extend or limit development on the individual case by asking the attending physician
            to submit the attending physician's objective findings establishing the severity of
            the patient's condition and the patient's immediate and/or long term therapeutic need
            for the equipment. The carrier may ask the attending physician for a statement of
            the therapeutic benefits the attending physician expects the patient to realize from
            the use of this equipment.
         
         Carriers establish safeguards to assure that payments are not made beyond the last
            month of medical necessity or, in the case of purchase, beyond the month which would
            complete reimbursement for the item if this comes first. For example, if medical necessity
            for an item is estimated by the physician at 2 months but it would require 4 payments
            to complete reimbursement, the carrier takes appropriate steps to assure that the
            periodic payments will be stopped at the end of the 2-month period.