Unna boots under Medicare: A6456 coverage, units and weekly changes

The code: A6456

CMS describes A6456 as:

Zinc paste impregnated bandage, non-elastic, knitted/woven, width greater than or equal to three inches and less than five inches, per yard

In plain terms: a non-elastic zinc paste bandage, at least 3 and under 5 inches wide, billed by the yard. A6456 is also on the Policy Article's list of codes that need an A1–A9 modifier for the number of qualifying wounds the code is used on.

What's covered

LCD L33831 covers a zinc paste impregnated bandage “for the treatment of venous leg ulcers that meet the statutory requirements for a qualifying wound,” which it defines in parentheses as “(surgically created or modified, or debrided).”

That's the same test every surgical dressing has to pass: a wound caused by, or treated by, a surgical procedure, or a wound after debridement. A venous leg ulcer on its own isn't enough; the record has to show it's a qualifying wound.

Weekly changes

The LCD is direct: “Dressing change frequency for A6456 is weekly.” For boots sent home, quantities follow from that weekly change and from the bandage each change uses, within the LCD's limit of no more than a month's supply at one time.

Billing per yard

The descriptor ends “per yard,” so units are yards of bandage, not rolls or boots. If a roll is divided into pieces, the Policy Article says “the code and quantity billed must represent the originally manufactured size and quantity.” Check the length on the product label, and confirm units with your billing staff.

When it isn't covered

The LCD says claims for A6456 used for venous insufficiency without a qualifying wound, or for other non-qualifying conditions, “will be denied as statutorily non-covered, no benefit.”

The Policy Article says the same of the other bandage types: they are “non-covered when used for non-qualifying conditions such as, strains, sprains, edema,” or in any situation other than as a dressing for a qualified wound.

Multi-layer compression systems

Compression bandages and multi-layer systems are covered only when used as a primary or secondary dressing over a qualifying wound (LCD L33831). The Policy Article covers moderate or high compression, conforming, self-adherent and padding bandages when they are “part of a multi-layer compression bandage system used in the treatment of a venous stasis ulcer” that meets the qualified-wound requirements.

A system isn't billed as a single item. When one is used for a venous stasis ulcer, “each component is billed using a specific code for the component.”

On replacement, the LCD says “Most compression bandages are reusable,” and replacement “would be no more than one per week unless they are part of a multi-layer compression bandage system.”

Other bandage codes

The LCD groups the bandage codes like this. Note that light compression covers three codes, A6448–A6450, one for each width band.

For conforming bandages, the LCD adds: “Conforming bandage dressing change is determined by the frequency of change of the selected underlying dressing.” Tubular dressings (A6457) appear in the LCD's code list and, like every code in the table, take an A1–A9 modifier.

In the office or sent home

Unna boots are usually applied in the office and left in place between visits. Where they're applied changes the billing:

• Applied as part of a billed service. When a treating practitioner applies surgical dressings as “part of a professional service that is billed to Medicare,” the Policy Article treats them as incident to that service. They “are not separately payable,” and “Claims for these dressings must not be submitted.”
• Sent home. If dressing changes are sent home with the patient, claims for them may be submitted, with the place of service for the patient's residence. “Place of Service Office (POS=11) must not be used.”

PCSS Unna boots

PCSS carries 4-inch Unna boots in two formulations, zinc oxide and calamine. At 4 inches, both fall inside A6456's width band: “greater than or equal to three inches and less than five inches.”

PCSS suggests A6456 for both. The A6456 descriptor begins “Zinc paste impregnated bandage,” so confirm the code for the calamine product with your billing staff.

For the layers around a boot, PCSS also carries non-bordered foam for use under wraps, sterile roll gauze (PCSS suggests A6446), and elastic tubular bandage and cohesive wrap for securing dressings (PCSS suggests A6457 and A6454). Confirm final coding with your billing staff.

Questions

Sources

Checked on October 6, 2026. Medicare policy changes; confirm current versions before relying on them. This page is general information, not billing, coding or legal advice.