Histocompatibility Testing — NCD 188 | CMS Coverage Update

CMS modified NCD 188 for histocompatibility testing, effective March 7, 2026. Here's what billing teams need to know.

The Centers for Medicare & Medicaid Services updated NCD 188 — the National Coverage Determination governing Medicare coverage of histocompatibility testing, including human leukocyte antigen (HLA) typing and matching. This policy covers testing in preparation for kidney transplants, bone marrow transplantation, blood platelet transfusions, and suspected ankylosing spondylitis. The CMS histocompatibility testing coverage policy does not list specific CPT or HCPCS codes, which creates documentation and billing challenges your team needs to address before the effective date.

Quick-Reference Table

CMS Histocompatibility Testing Coverage Criteria and Medical Necessity Requirements 2026

NCD 188 in the CMS Medicare system covers histocompatibility testing for four specific clinical situations. The policy is straightforward for three of them. The fourth — ankylosing spondylitis — is where your denials are going to come from.

For kidney transplant preparation, bone marrow transplantation preparation, and blood platelet transfusion preparation, CMS covers HLA testing when it is reasonable and necessary for the patient. That "reasonable and necessary" language is standard Medicare medical necessity language, but it still means you need documentation in the chart that supports why the test was ordered.

For ankylosing spondylitis, the bar is higher. The CMS coverage policy only covers HLA testing for this indication when other diagnostic methods would not be appropriate or have already produced inconclusive results. And the policy is explicit: you must request documentation from the ordering physician supporting medical necessity in every ankylosing spondylitis case. Every one. Not just the ones that look borderline.

This is where histocompatibility testing billing gets complicated. The transplant and transfusion indications are relatively clean — the clinical context makes medical necessity obvious and the documentation usually exists in the record. Ankylosing spondylitis is different. You're billing for a genetic marker test on a rheumatology patient, and CMS wants proof that standard diagnostic workup didn't get the job done first.

If your lab or specialty practice sees a meaningful volume of HLA-B27 tests ordered for suspected ankylosing spondylitis, talk to your compliance officer before the effective date of March 7, 2026. The prior authorization question isn't directly addressed in this policy, but the documentation burden functions similarly — you need the physician's justification on file before the claim goes out, not after the denial lands.

The reimbursement risk here is real. A claim for HLA testing tied to ankylosing spondylitis without supporting documentation isn't just likely to deny — it potentially creates a compliance exposure if it's a pattern across your claims.

CMS Histocompatibility Testing Exclusions and Non-Covered Indications

NCD 188 doesn't use explicit "not covered" or "experimental" language for additional indications. But read the coverage list as a fence, not a floor.

The policy covers HLA testing for four indications only. Testing ordered for any other reason — general genetic screening, ancestry-related testing, or unspecified immunological workup — falls outside this coverage policy. Those claims won't just be denied; they'll be denied as non-covered services, which is a different conversation with your payer and your patient.

The ankylosing spondylitis carve-out also functions as a soft exclusion. If the physician orders HLA-B27 testing for a patient with a suspected diagnosis but hasn't documented that other methods were tried or ruled out, that claim is in serious jeopardy. The policy doesn't call it experimental — it just doesn't cover it unless the documentation threshold is met.

Coverage Indications at a Glance

CMS Histocompatibility Testing Billing Guidelines and Action Items 2026

The modified NCD 188 doesn't add new indications or loosen restrictions. It tightens the documentation expectation, particularly for ankylosing spondylitis. Here's what your billing team needs to do.

CPT, HCPCS, and ICD-10 Codes for Histocompatibility Testing Under NCD 188

Covered CPT/HCPCS Codes

The NCD 188 policy document does not list specific CPT or HCPCS codes. This is a significant gap for histocompatibility testing billing.

In practice, HLA typing and matching tests are billed using a range of molecular pathology and immunology codes — but CMS has not enumerated them in this policy. That means your team cannot rely on the NCD itself to validate code selection. You're responsible for confirming that the codes you bill map to a covered indication and meet the medical necessity standard.

Work with your laboratory billing specialist to confirm which CPT codes your lab uses for HLA typing, HLA matching, and HLA-B27 testing. Then verify that each code has been reviewed against current CMS billing guidelines and any applicable MAC local coverage determinations. If you're unsure which codes apply to your specific test menu, consult your compliance officer or a billing consultant with laboratory specialty experience before the March 7, 2026 effective date.

Key ICD-10-CM Diagnosis Codes

NCD 188 does not list specific ICD-10-CM codes. However, based on the covered indications in the policy, your diagnosis codes should align with the following clinical scenarios:

• Kidney transplant preparation
• Bone marrow transplantation preparation
• Blood platelet transfusion preparation (especially repeat transfusions)
• Suspected ankylosing spondylitis with documentation that other diagnostic methods were inappropriate or inconclusive

Your coding team should confirm diagnosis code selection against current ICD-10-CM guidelines. Mismatched diagnosis codes — particularly for ankylosing spondylitis claims — are a direct path to claim denial under this policy.