Evidence of Medical Necessity for Oxygen (Rev. 1, 10-01-03)

by  Jared Staheli
June 18th, 2015

Oxygen coverage is determined by the results of an arterial blood gas or oximetry test. A CMN for oxygen equipment must include results of specific testing before coverage can be determined.

Suppliers that bill electronically may transmit initial, revised, and recertification CMNs by electronic media using CMS-established standard formats. Information transmitted from a revised or recertification Form CMS-484 must accompany the first claim for monthly benefits submitted after the supplier has received the hard copy Form CMS-484 from the certifying physician. If the supplier submits Form CMS-484 information to the contractor electronically, the supplier must keep the paper certification readily available so that it may be promptly furnished to the contractor if requested for purposes of audits of medical necessity documentation.

Blood Oxygen Testing

The medical necessity of home oxygen is documented by the results of a blood oxygen test. The blood oxygen test may be either an arterial blood gas or an oximetry test. The following timeliness requirements must be met. Initial Certification: Groups I and II: Must be tested within 30 days prior to the date of initial certification. If the oxygen is begun immediately following discharge from an acute care facility, the test must be within two days prior to discharge.


Group I: Retesting requirements are to be determined by the contractor.

Group II: Must be retested between the 61st - 90th day after the date of the initial certification.

Revised Certifications:

Group I and II: Must be tested within 30 days prior to the date of the revised certification if the initial certification specified a length of need that is less than lifetime.

Physician Evaluation

Initial Certification:

Groups I and II: Must be seen and evaluated by the treating physician within 30 days prior to the date of initial certification


Group I and II: Must be seen and re-evaluated by the treating physician within 90 days prior to any recertification date.

A. Initial Certifications

In reviewing the claim and the supporting data, contractors compare certain items, especially pertinent dates of treatment. For example, the start date of home oxygen coverage cannot precede the date of prescription or the date of the test(s) whose results establish that the special coverage criteria are met. Once coverage is established, the estimated length of need in Section B on the Form CMS-484, and the circumstances and the results of testing that established the medical necessity at the start of home oxygen therapy, determines the recertification schedule.

Definitions of "Group" based on blood gas values:

Group I - An arterial PO2 at or below 55 mm Hg, or arterial blood oxygen saturation at or below 88 percent.

Group II - An arterial PO2 is 56 to 59 mm Hg or arterial blood oxygen saturation is 89 percent.

Group III - An arterial PO2 at or above 60 mm Hg, or arterial blood oxygen saturation at or above 90 percent.

When oxygen is prescribed in an institution, in order to establish medical necessity it is necessary that the institution would have to recheck the oxygen level no sooner than 2 days before discharge.

Clinical documentation will be reviewed to confirm the fact that the prescribing of continued oxygen was based upon the "chronic stable state" (was done while the patient was in a chronic stable state - i.e., not during a period of acute illness or an exacerbation of the patient's underlying disease) of the patient.

Contractors verify that the information shown on or accompanying the Form CMS-484 or other CMN supports the need for oxygen as billed.

When both arterial blood gas (ABG) and oxygen saturation (oximetry) tests have recently been performed on the same day, suppliers report only the ABG result. That test is generally acknowledged as the more reliable indicator of hypoxemia.

Test results from oximetry tests performed by a DME supplier, or anyone financially associated with or related to the DME supplier, are not acceptable.

Values in Group III establish a rebuttable presumption of non-coverage. The CMN must be supplemented by additional documentation from the treating physician designed to overcome this presumption and justify the oxygen order, including a summary of other, more conservative therapy that has not relieved the patient's condition. Claims with such documentation are referred to the contractor's medical director for the coverage determination.

The following types of claims are denied without further development:

• Claims where the only qualifying test results came from oximetry tests conducted by a DME suppliers other than a hospital;

• Claims lacking information necessary to justify coverage;

• Hard copy claims where the CMN or Form CMS-484 lacks the treating physician's signature; or

• Electronic claims where the CMN or Form CMS-484 fails to indicate that the treating physician's handwritten signature is on file in the supplier's office.

An initial CMN is also required when there has been a break in medical necessity of 60 days plus whatever days remained in the rental month during which the oxygen was discontinued. (This indication does not apply if there was just a break in billing because the patient was in a hospital, nursing facility, hospice, or HMO, but the patient continued to use oxygen during that time.)

B. Revised Certifications

Contractors encourage treating physicians to file timely, revised CMNs or Form CMS- 484s through the supplier if their order for oxygen changes.

A revised CMN is necessary when:

1. The prescribed maximum flow rate changes from one of the following categories to another: (a) less than 1 LPM, (b) 1-4 LPM, (c) greater than 4 LPM. If the change is from category (a) or (b) to category (c), a repeat blood gas study with the beneficiary on 4 LPM must be performed within 30 days prior to the start of the greater than 4LPM flow.

2. Portable oxygen is added subsequent to initial certification of a stationary system. In this situation, there is no requirement for a repeat blood gas study unless the initial qualifying study was performed during sleep, in which case a repeat blood gas study must be performed while the patient is at rest (awake) or during exercise.

3. The initial certification specified an estimated length of need that is less than lifetime and the physician wants to extend the certification.

4. There is a new treating physician (no new testing is required).

Contractors do not adjust payments on oxygen claims unless a revised certification documents the necessity for the change. Contractors timely adjust payments, if necessary, for services since the oxygen prescription was changed.


Evidence of Medical Necessity for Oxygen (Rev. 1, 10-01-03). (2015, June 18). Find-A-Code Articles. Retrieved from https://www.findacode.com/articles/evidence-of-medical-necessity-for-oxygen-rev-1-10-01-03-26726.html

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