Remember: ALWAYS BILL MEDICARE FOR A COVERED SERVICE. As a chiropractor, the only covered service in Medicare is the manual manipulation. However, the question was how to bill, so let's get to that.
As a Fee-For-Service Non-participating Provider in Medicare, you must accept assignment on a patient with Medicare Medicaid. You are allowed to collect unmet deductibles for Medicare. (Most of the time we take a small monthly payment plan for these individuals to meet that as they are on a budget.) They are on a fixed income and have met certain income criteria to be on the federal programs, no matter what the age. You must bill the covered service (the chiropractic adjustment) and mark box 13 as signed and 27 as accept assignment. For all other services you provide (that are not covered such as x-rays and therapies) make sure to have them sign the ABN notifying them at the time that these are not covered services, you are not required to bill those, and you may collect payment for those services.
Reference for Medi-Medi payment/billing requirements: (https://www.cms.gov/Outreach-and-Education/Medicare-Learning-Network-MLN/MLNProducts/downloads/Medicare_Beneficiaries_Dual_Eligibles_At_a_Glance.pdf)
"Assignment - You must accept assignment for services furnished to dual eligible beneficiaries. Assignment means that you are paid the Medicare-allowed amount as payment in full for all Part B claims for all covered services for all Medicare beneficiaries. You may not collect from the beneficiary any amount other than the unmet deductible and coinsurance. Prohibited Billing Under Section 1902(n)(3)(B) of the Social Security Act, as modified by Section 4714 of the Balanced Budget Act of 1997, Medicare and Medicaid payments you receive for furnishing services to a QMB are considered payments in full. You may not balance bill QMBs for any Medicare cost sharing (including deductibles, coinsurance, and copayments) for these services. You are subject to sanctions if you bill a QMB for amounts above the Medicare and Medicaid payments (even when Medicaid pays nothing)."
Reference for covered services: (https://www.cms.gov/Regulations-and-Guidance/Guidance/Manuals/Downloads/bp102c15.pdf)
"30.5 - Chiropractor’s Services (Rev. 23, Issued: 10-08-04, Effective: 10-01-04, Implementation: 10-04-04) B3-2020.26 A chiropractor must be licensed or legally authorized to furnish chiropractic services by the State or jurisdiction in which the services are furnished. In addition, a licensed chiropractor must meet the following uniform minimum standards to be considered a physician for Medicare coverage. Coverage extends only to treatment by means of manual manipulation of the spine to correct a subluxation provided such treatment is legal in the State where performed. All other services furnished or ordered by chiropractors are not covered. If a chiropractor orders, takes, or interprets an x-ray or other diagnostic procedure to demonstrate a subluxation of the spine, the x-ray can be used for documentation. However, there is no coverage or payment for these services or for any other diagnostic or therapeutic service ordered or furnished by the chiropractor. For detailed information on using x-rays to determine subluxation, see §240.1.2. In addition, in performing manual manipulation of the spine, some chiropractors use manual devices that are hand-held with the thrust of the force of the device being controlled manually. While such manual manipulation may be covered, there is no separate payment permitted for use of this device."
Reference for ABN use: (https://www.cms.gov/Outreach-and-Education/Medicare-Learning-Network-MLN/MLNProducts/downloads/Chiropractors_fact_sheet.pdf)
"Option #2: A beneficiary selects option #2 when s/he agrees to pay out of pocket for the service in question and does not want a claim sent to Medicare. In accordance with the ABN, the provider would not file a claim, and the beneficiary would not have appeal rights since no claim is being submitted. (Please note that the patient can change his/her mind at a future time and request the claim be submitted.)"