SNF Part A vs Part B Wound Care Billing: Which Applies?
When wound care in a SNF is billed under Medicare Part A vs Part B — the coverage rules, who bills, and why getting this wrong means you don't get paid.
Damon Ebanks
Medipyxis
SNF Part A vs Part B Wound Care: Which Applies?
The short answer: if the patient is in a Medicare Part A covered stay, the SNF's per-diem rate covers wound care and you generally cannot bill Medicare separately. If the patient is in a Part B stay -- either because Part A benefits have exhausted or the patient does not qualify for a skilled stay -- you bill Medicare Part B directly as the treating provider.
Getting this wrong is not a soft error. Billing Part B for a patient who is under an active Part A stay results in an automatic denial. The claim is rejected because Medicare has already paid the facility for that care through the consolidated billing rules. There is no appeal path that reverses this -- the billing was categorically wrong, not clinically insufficient.
Part A: Wound Care Included in the Per-Diem
When a resident is in a Medicare Part A covered skilled nursing stay, the SNF receives a bundled per-diem payment that covers virtually all services the resident receives. This includes wound care -- debridement, wound assessments, dressing changes, and most supplies. The SNF is responsible for arranging and paying for these services, whether they are provided by facility staff or by an outside wound care provider.
If you are the outside wound care provider treating a Part A patient, your billing arrangement is with the SNF, not with Medicare. The SNF pays you directly (typically under a contract or per-visit arrangement), and the SNF absorbs your charges into their per-diem rate. You do not submit a claim to Medicare for this patient.
Part A coverage applies during the first 100 days of a qualifying skilled nursing stay, though the coverage window depends on the patient meeting skilled care criteria and the benefit period not being exhausted.
Part B: You Bill Medicare Directly
Part B billing applies when the patient is in the SNF but is not under a Part A covered stay. This happens in three common scenarios:
- Part A benefits exhausted. The patient has used their 100-day skilled nursing benefit for the current benefit period. They remain in the facility as a long-term care resident, and their clinical services -- including wound care -- are billed under Part B.
- Non-covered stay. The patient is in the SNF for custodial care rather than a skilled nursing need. They were never admitted under Part A for this stay. Part B applies from the first day.
- Part A ended, wound care continues. The patient had a Part A stay that ended (discharged from skilled services), but they remain in the facility and still need wound care. The transition from Part A to Part B coverage is the point where your billing responsibility shifts from the SNF to Medicare.
Under Part B, you bill Medicare directly using standard wound care CPT codes -- E/M visits, debridement, skin substitute application -- with place of service code 31 (Skilled Nursing Facility).
How to Determine Which Applies
Before every SNF visit, verify the patient's coverage status. This is not a one-time check -- a patient's status can change from Part A to Part B between visits. The verification process:
Ask the facility. The SNF's billing department or MDS coordinator can confirm whether a patient is in a Part A covered stay or a Part B stay. This should be a routine question before every wound care encounter, not an assumption based on the prior visit.
Check benefit days remaining. If the patient is on Part A, ask how many covered days remain. A patient on day 95 of a 100-day benefit is about to transition to Part B, which changes who you bill and how you document the encounter.
Confirm admission status. Some patients are in the SNF under observation status or custodial care, neither of which triggers Part A consolidated billing. Admission status determines billing pathway -- do not assume skilled nursing facility equals Part A coverage.
The Common Billing Mistake
The most expensive error in SNF wound care billing is submitting a Part B claim for a patient who is under an active Part A stay. This happens most often when the wound care provider does not verify the patient's coverage status before the visit and defaults to billing Part B because that is what they billed on the previous encounter.
The denial is automatic and clean -- Medicare's system sees that the patient has an active Part A stay and rejects the Part B claim under consolidated billing rules. The provider then has no path to payment: Medicare will not pay the Part B claim, and the SNF may not have a contractual obligation to pay the provider for an unauthorized visit.
The prevention is straightforward: verify every patient's coverage status before every visit. Build the verification step into your pre-visit workflow, not your post-visit billing process.
For a complete playbook on building SNF referral partnerships, see the SNF wound care referral playbook. For guidance on setting up payer enrollment to bill Part B directly, see the wound care payer enrollment guide.