A CMN, or Certificate of Medical Necessity, is a standardized form that was used in the Medicare system to document why a patient needs a specific piece of durable medical equipment (DME). It served as proof that items like home oxygen systems, hospital beds, or compression devices were medically required, not just convenient. If you’re encountering this term now, there’s an important update: CMS (the federal agency that runs Medicare) discontinued CMNs for all claims with dates of service on or after January 1, 2023, replacing them with a simpler documentation process.
What a CMN Was Used For
Medicare doesn’t automatically pay for medical equipment. Before covering items like a wheelchair, oxygen concentrator, or electrical nerve stimulator, the program needs evidence that the equipment is genuinely necessary for the patient’s condition. That’s the role the CMN filled. A treating physician would complete the form, answering specific questions about the patient’s diagnosis, functional limitations, and why the equipment was needed. The completed CMN then traveled with the insurance claim so that Medicare’s payment contractors could verify coverage.
The types of equipment that historically required a CMN or a related form called a DME Information Form (DIF) included:
- Oxygen and oxygen equipment for long-term use
- Oxygen equipment for children 12 and under
- External infusion pumps (excluding insulin pumps)
- Pneumatic compression devices
- Seat lift mechanisms
- TENS units (transcutaneous electrical nerve stimulation)
- Osteogenesis stimulators (devices that promote bone healing)
Without a properly completed CMN, claims for these items would typically be denied, leaving the patient or supplier responsible for the cost.
Why CMS Discontinued CMNs
After gathering feedback from healthcare providers, suppliers, and other stakeholders, CMS determined that CMNs were burdensome and duplicative. The information they captured was largely already available in the patient’s medical record or on the claim itself. Physicians were spending time filling out paperwork that restated what their clinical notes already documented, and suppliers were chasing signatures and correcting form errors that delayed patient access to equipment.
CMS officially ended the requirement for CMNs and DIFs for any claim with a date of service on or after January 1, 2023. Suppliers still need to submit CMN data for older claims that predate that cutoff, but no new CMNs are being generated.
What Replaced the CMN
The CMN didn’t disappear without a replacement. Medicare now relies on a Standard Written Order (SWO) as the core document linking a patient to their prescribed equipment. An SWO is simpler and more flexible than the old CMN, but it still has specific required elements:
- Patient identification: the beneficiary’s name or Medicare ID number
- Order date
- Item description: a general description of the equipment (for example, “wheelchair” or “hospital bed”), a billing code, or a brand name and model number
- Quantity: how many units to dispense, if applicable
- Treating practitioner’s name or provider ID number
- Treating practitioner’s signature: must be handwritten or an acceptable electronic equivalent. Signature stamps and date stamps are not allowed.
If the order covers equipment with separately billed accessories or options, each one needs to be listed individually on the SWO. The same applies to supplies. Medicare contractors can request the completed SWO at any time, so suppliers must keep it on file and be ready to produce it.
How This Affects Patients
If you’re a Medicare beneficiary waiting on equipment like a home oxygen system or a power wheelchair, the shift away from CMNs is mostly good news. The old process often created delays: a supplier would submit a claim, realize the CMN was incomplete or had an error, then go back to the physician’s office for corrections. That back-and-forth could add days or weeks before equipment arrived.
The SWO process is leaner, but medical necessity still has to be proven. Your physician’s clinical notes, test results, and other records in your medical chart now carry that weight directly. If Medicare audits the claim, the documentation in your chart is what they’ll review. So while you won’t encounter a CMN form anymore, your doctor still needs to clearly record why you need the equipment in their notes.
Why You Might Still See the Term
Even though CMNs are no longer required for new claims, the term hasn’t vanished from healthcare. Many electronic health record systems and billing software platforms still reference CMNs in their workflows because they were a fixture of DME billing for decades. Some private insurers also use their own versions of medical necessity certificates that function similarly, even if they don’t use the exact CMS form. And if you’re dealing with any claim that dates back to before January 2023, the CMN rules from that era still apply.
You may also encounter the abbreviation in a completely different context. In dermatology and pediatrics, CMN can stand for congenital melanocytic nevus, a type of pigmented birthmark present at birth. The meaning is usually clear from context, but if you searched this term after seeing it on a medical bill or insurance document, the Certificate of Medical Necessity is almost certainly what it refers to.