HCPCS code A4423: Closed ostomy pouch, locking flange with filter

Key Takeaways

HCPCS code A4423 covers a closed ostomy pouch for a barrier with a locking flange and a built-in filter, billed as one unit in a 2-piece system

A4423 is not A4424 with the filter removed. A4424 is a one-piece drainable pouch with the barrier already attached, a different product entirely

Ostomy supplies fall under Medicare’s prosthetic device benefit, and the KX modifier does not apply to A4423 the way it does to other DME categories

Practice management software like Pabau keeps physician orders, diagnosis codes, and claim status connected, so missing information surfaces before a claim goes out

HCPCS code A4423 covers a closed ostomy pouch built for a barrier with a locking flange and an integrated filter, billed as one unit in a 2-piece system. Miss any one of those three details on a claim, and Medicare denies it.

The trouble is, A4423 sits inside a dense cluster of near-identical A44xx codes, and one comparison keeps tripping billing teams up: A4423 against A4424. They are not the same pouch with a filter added or removed. A4424 belongs to a different pouch family altogether, and treating the two as interchangeable is how a clean-looking claim gets rejected for the wrong reason.

What HCPCS code A4423 covers

HCPCS code A4423 is a Level II supply code maintained by the Centers for Medicare and Medicaid Services (CMS). It sits in the HCPCS A-series for medical and surgical supplies.

The official long descriptor is specific for a reason: Ostomy pouch, closed; for use on barrier with locking flange, with filter (2-piece), each. Every phrase in that descriptor is a billing qualifier, not filler wording.

Three features decide whether A4423 is the correct code

A4423 describes a closed-end pouch. Unlike a drainable pouch, a closed pouch is sealed at the bottom and thrown away after one use rather than emptied and reattached.

That design suits patients with firmer, more predictable stoma output. Most colostomy patients fall into this group, while looser output usually calls for a drainable system instead.

Three product features together decide whether A4423 is the right code:

• Closed design: the pouch has a sealed bottom with no drain outlet. It gets used once and discarded, rather than emptied in place.
• Locking flange: the pouch clicks and locks onto the barrier wafer. A floating or non-locking flange relies on pressure fit instead, and that difference alone moves the claim to a different code.
• Integrated filter: a built-in charcoal filter vents gas and cuts odor. Not every closed pouch includes one, and whether the filter is present is the detail that separates A4423 from its closest neighbor.

All three features have to match the dispensed product before A4423 goes on a claim. Supplying a closed pouch with a non-locking flange, or a locking-flange pouch without a filter, calls for a different code entirely. Tracking inventory and supply usage at the product level is the most reliable way to confirm the right code before submission.

Many new ostomates also practice pouch changes with an occupational therapist before managing the routine alone. A rehab practice running occupational therapy software sees the same product-matching questions from a self-care angle, not a billing one.

A4423 is not A4424 with the filter removed

The A4419-A4427 range covers several ostomy pouch configurations, and mixing up flange type or pouch type is the leading cause of claim rejection here. Three variables separate these codes: pouch type (closed vs. drainable), flange type (locking vs. non-locking), and whether a filter is built in.

The realistic miscoding pattern runs in two directions, not the one many billing guides describe. Billing A4423 when the barrier doesn’t lock means the correct code was A4419. Billing it when no filter is present means the correct code was A4420.

A4424 isn’t a close call at all. It’s a one-piece drainable pouch with the barrier already attached, built for a different stoma output pattern altogether. If a comparison chart says A4423 and A4424 differ only by a filter, that chart is wrong, and it’s worth double-checking every other comparison in it too.

What A4423 pays under the 2026 fee schedule

HCPCS code A4423 is reimbursed under the CMS DMEPOS fee schedule, not the physician fee schedule. Rates are locality-adjusted, so the allowable amount varies by the patient’s geographic region and updates each January.

Third-party fee schedule tools can lag the official CMS update, so treat any figure from them as a starting point, not the final billed amount. Suppliers billing above the fee schedule allowable may not balance-bill Medicare beneficiaries for the excess.

Medicare’s coverage rules for A4423

Coverage for A4423 runs through CMS Policy Article A52487 (Ostomy Supplies) and its companion Local Coverage Determination, L33828. The order usually starts in primary care, so a practice running GP clinic software needs the same order-detail discipline as the supplier filling it. Good compliance management tools help practices stay aligned with these payer rules at the point of supply, not after a denial arrives.

To qualify for Medicare coverage, the beneficiary must meet all of the following:

• A physician or another qualified treating practitioner has ordered the ostomy supplies
• The patient has a qualifying ostomy diagnosis (colostomy, ileostomy, or urostomy)
• The patient is not an inpatient, or a resident of a facility responsible for supplying the item
• The supplier is enrolled as a Medicare DMEPOS supplier

The ICD-10 codes that support an A4423 claim

The following ICD-10-CM diagnosis codes are the codes most consistently cited to establish medical necessity for ostomy supply claims, including A4423. Verify current applicability against the CDC/NCHS ICD-10-CM web tool before submitting claims.

Z93.3 and Z93.2 are the most commonly used supporting diagnoses for closed ostomy pouch claims. K94.00 and K94.10 cover a general, unspecified colostomy or enterostomy complication, while K94.03 and K94.13 apply when the complication is specifically a malfunction.

The Z43 codes cover a routine encounter for ostomy attention rather than a complication. Some MACs maintain local coverage articles that expand this list further, so always verify with your specific MAC before submitting.

How an A4423 claim moves from order to payment

A biller who has handled ostomy claims for a while can usually predict where an A4423 claim will stall before it happens. Here is the realistic path from order to paid claim.

1. The physician or another qualified practitioner writes an order naming the ostomy supply type, quantity, and frequency, not a generic “ostomy supplies as needed” note.
2. The supplier confirms the dispensed product against that order, checking pouch type, flange type, and filter before it ships.
3. The biller matches the confirmed product to a HCPCS code. A4423 applies only when all three features line up.
4. The claim goes out with a qualifying ICD-10 code, the ordering practitioner’s details, and proof of delivery on file.
5. The DME MAC processes the claim under the prosthetic device benefit and pays 80% of the allowed amount, with the patient or a secondary payer covering the rest.

Most denials trace back to step two or three, not step four or five. A claim with perfect paperwork still gets rejected if the product-to-code match was wrong from the start.

Do you need a KX modifier on A4423? No, and here’s why

Plenty of DME billing guides say to append modifier KX whenever a supply claim nears a coverage or quantity threshold. For A4423 and the rest of the ostomy pouch family, that instruction does not apply.

CMS Policy Article A52487 does not require the KX modifier for ostomy supply codes. Coverage instead rests on the physician’s order, a qualifying diagnosis, and an enrolled DMEPOS supplier being on file at billing time, not on a modifier. Appending KX to A4423 out of habit does not help the claim, and it is not correct coding.

The KH, KI, and KJ modifiers are a different mismatch entirely. They mark the billing period for a capped rental item: month one, months two and three, months four through 13. A4423 is a purchased consumable, not a rental, so none of those modifiers belong on this claim either.

What does apply is the AU modifier. It applies only to separate ostomy accessory codes, like tape and adhesive (A4450, A4452, A5120), when they are billed alongside a pouch, not to A4423 itself.

Before you submit an A4423 claim, run this checklist

Incomplete documentation is the second most common reason A4423 claims fail, right after a mismatched product code. Run through this list before the claim goes out:

• Physician or practitioner order on file, naming the supply type, quantity, and frequency, not a generic order
• Diagnosis code confirmed against the ostomy type in the medical record, matching Z93.2, Z93.3, Z93.6, or the relevant K94 complication/malfunction code
• Barrier type confirmed as locking flange, not floating or non-locking, in the order itself and not only on the product sheet
• Quantity checked against the current monthly allowance, with a physician’s written explanation attached if the order exceeds it
• Proof of delivery on file, confirming the patient received what was billed

The mistakes that get A4423 claims rejected

A few patterns show up again and again in denied A4423 claims:

• Assuming A4423 and A4424 are close substitutes. They come from different pouch families, so mixing them up counts as a wrong-product claim, not a minor coding slip.
• Appending KX or a rental modifier out of habit, carried over from other DME billing, when neither applies to a purchased ostomy supply.
• Relying on the manufacturer’s product sheet instead of explicit locking-flange language in the physician’s order.
• Billing above the monthly quantity allowance without the physician’s written explanation for the increased usage attached to the file.
• Using a general “unspecified complication” code when the documentation describes something more specific, like a malfunction, or the reverse.

Medicaid and commercial payers set their own A4423 rules

Medicaid coverage for A4423 is state-determined. Most state Medicaid programs cover ostomy supplies, but quantity limits, prior authorization rules, and formulary restrictions vary by state.

There is no uniform federal Medicaid standard for closed ostomy pouch coverage, so verify directly with each state program before supplying.

Commercial payers often diverge from Medicare in a few specific ways:

• Prior authorization: many commercial plans require it for DMEPOS ostomy supplies, including A4423, while Medicare does not for standard quantities.
• Quantity limits: commercial allowances can be more or less generous than Medicare’s.
• Formulary restrictions: some payers limit coverage to specific brands or preferred suppliers.
• Documentation standards: commercial requirements can differ from CMS standards, so check each plan’s DMEPOS billing guidelines directly.

For practices billing several payer types, keeping HIPAA-compliant records aligned across payer types prevents documentation issues that only surface at audit.

How Pabau keeps A4423 claims from stalling

Most A4423 denials start upstream, in how the supply order gets captured and matched to a code, rather than in the claim form itself.

Practice management software like Pabau keeps the physician’s order, the diagnosis code, and the claim status connected in one record.

Pabau’s claims management software checks that required insurer-submission fields are complete before the send action unlocks. It also gives a status dashboard, so a missing piece of documentation surfaces before the claim goes out, not after a denial comes back.

Keep ostomy claims from stalling in review

Pabau connects physician orders, diagnosis codes, and claim status in one workflow, so incomplete documentation surfaces before you submit, not after a denial comes back.

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The bottom line on billing HCPCS code A4423

Billing HCPCS code A4423 correctly comes down to three details: a closed pouch, a locking flange, and a built-in filter. Miss one, and the claim belongs to a different code, usually A4419, A4420, or an unrelated pouch family like A4424.

None of that requires a KX modifier or a rental modifier. It requires a physician’s order that names the barrier type explicitly and a diagnosis code that matches the documentation. The claim file also needs to be complete before it goes out the door. Practice management software like Pabau keeps those pieces connected instead of scattered across separate systems.

Book a demo to see how Pabau supports ostomy and other DMEPOS billing workflows for supply-intensive practices.

Continue your research

Need a drainable pouch instead? A4425 covers the drainable, non-locking-flange pouch with a filter, a different pouch family from the closed A4423.

Need the drainable, locking-flange equivalent? A4427 is A4423’s drainable counterpart.

Want fewer missing-documentation denials? Pabau’s claims management software keeps orders and claim status connected in one record.

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