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What this equipment is
E0431 is the HCPCS code for portable gaseous oxygen — compressed oxygen in tanks or canisters used outside the home setting. It's for patients who require continuous oxygen but need to leave the house — walking to appointments, traveling, or maintaining normal daily activities.
Unlike stationary oxygen (E1390), portable oxygen is not subject to the 36-month equipment rental cap. It's billed as a supply (contents and container rental combined) on a monthly basis.
Medicare coverage criteria
- Patient meets stationary oxygen criteria. E0431 is only covered if the patient meets the same qualifying criteria as stationary oxygen (E1390): PaO2 ≤55 mm Hg or O2 sat ≤88% at rest, or ≤59/89% with qualifying comorbidities. A patient must first qualify for stationary oxygen before portable oxygen is covered.
- Patient leaves the home. Medicare requires documentation that the patient leaves the home for brief periods and needs portable oxygen to maintain their oxygen saturation outside the home setting. This is documented in the CMN.
- Physician order. Must specify portable oxygen, flow rate, and that the patient leaves the home.
What actually causes denials in DME back offices
- No corresponding stationary oxygen coverage. Billing E0431 without an active E1390 claim or proof the patient meets stationary oxygen criteria is a near-guaranteed denial. The portable system is an add-on to stationary therapy, not a standalone item.
- Stationary oxygen cap expired. After the 36-month E1390 rental cap, portable oxygen contents continue — but only if the patient's stationary oxygen coverage was valid and the patient continues to need oxygen. Billing E0431 without documenting the stationary rental history can trigger denials.
- Flow rate mismatch. The portable oxygen flow rate must match the patient's documented needs. If the patient is on 2 L/min stationary and 0.5 L/min portable, the billing code and quantity must reflect that.
- Patient doesn't leave the home. Medicare specifically limits E0431 to patients who leave the home. If there's no documentation that the patient actually uses portable oxygen outside the home, the payer can deny on audit.
Documentation checklist
- Stationary oxygen qualification (PaO2 or O2 sat test within 30 days of order)
- CMN documenting patient leaves the home and needs portable oxygen
- Physician order specifying flow rate and portable use
- Proof of delivery
- Stationary oxygen device history on file
Reimbursement note: E0431 reimbursement is a combination of container/harness rental and oxygen contents. Medicare allows approximately $100–$160/month for portable gaseous oxygen depending on region and flow rate. Commercial payer rates vary by contract. E0431 is one of the few oxygen-related codes that continues to be billable after the 36-month equipment cap — this makes it an important revenue item for oxygen suppliers managing a long-term patient base.
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Frequently asked questions
Can I bill E0431 if the patient only uses portable oxygen and no stationary system?
Technically, Medicare requires the patient to first qualify for stationary oxygen before portable is covered. In practice, if the patient meets the oxygen saturation criteria and the physician documents a need for portable use (patient leaves home regularly), E0431 can be billed. The key is documenting that the qualifying oxygen level has been established, even if stationary therapy isn’t actively being used.
Is there a rental cap on E0431 like there is on E1390?
No. Portable gaseous oxygen (E0431) has no 36-month rental cap. The equipment rental and contents are billed monthly as long as medical necessity continues. This is why E0431 remains an important billing code after the stationary oxygen cap expires.
What is the difference between E0431 and E0434?
E0431 = portable gaseous oxygen system (compressed gas). E0434 = portable liquid oxygen system. Liquid systems are less commonly used today — they require special equipment and have more logistical complexity. Most suppliers bill E0431 for portable oxygen. Coverage rules are similar for both codes.