CMS Modified NCD 257 for Lymphocyte Mitogen Response Assays, Effective January 9, 2026 — Here's What Billing Teams Need to Do

The Centers for Medicare & Medicaid Services updated NCD 257, the National Coverage Determination governing Medicare coverage of lymphocyte mitogen response assays, effective January 9, 2026. This modification clarifies when the test is covered — and draws a hard line against billing it for cancer treatment monitoring. The policy does not list specific CPT or HCPCS codes, which creates its own documentation challenges your team needs to anticipate.

Quick-Reference Table

CMS Lymphocyte Mitogen Response Assay Coverage Criteria and Medical Necessity Requirements 2026

NCD 257 in the CMS Medicare system covers the lymphocyte mitogen response assay as a diagnostic laboratory test — but only under specific conditions. CMS defines this test as a measure of immune response using a patient's peripheral blood lymphocytes. The coverage policy is narrow, and the medical necessity bar is specific.

CMS covers the lymphocyte mitogen response assay when it is medically necessary to do one of two things: assess lymphocytic function in a patient with a diagnosed immunodeficiency disease, or monitor immunotherapy. Both of these are affirmative, documented clinical purposes. The word "diagnosed" matters here — a working diagnosis or clinical suspicion is not enough. The immunodeficiency disease must be established in the medical record before the test is ordered.

The coverage policy does not mention prior authorization requirements for this test. That said, medical necessity documentation is your real liability. If a claim comes back for medical review, CMS auditors will look for the immunodeficiency diagnosis in the chart — not just on the claim form. Make sure the ordering provider's notes support the test before you bill.

Ask your compliance officer to confirm whether your Medicare Administrative Contractor has issued a local coverage determination that adds further documentation requirements on top of NCD 257. MACs can be more restrictive than the national policy, and some have published LCDs for immunology testing that could affect reimbursement on these claims.

CMS Lymphocyte Mitogen Response Assay Exclusions and Non-Covered Indications

Here is the clear line CMS draws: this test is not covered when used to monitor cancer treatment. CMS classifies that use as experimental. That single exclusion has real billing implications.

If your oncology or hematology team orders a lymphocyte mitogen response assay to track how a cancer patient is responding to treatment — even chemotherapy-related immune monitoring — Medicare will deny the claim. The experimental designation is not a soft exclusion. It is a hard non-coverage determination under NCD 257.

The real issue here is that lymphocyte function testing does have clinical relevance in cancer patients. Oncologists use immune monitoring as part of treatment management. But CMS has not moved from its experimental designation for that specific indication. Until that changes in a future NCD update, billing for cancer treatment monitoring creates claim denial exposure every time.

Watch for orders that blend indications. A patient might have both an immunodeficiency diagnosis and an active cancer diagnosis. The covered indication has to be the documented clinical reason for the test — not a secondary diagnosis you use to qualify a claim that was really ordered for cancer monitoring. Your compliance officer should weigh in on mixed-indication cases before you bill.

Coverage Indications at a Glance

CMS Lymphocyte Mitogen Response Assay Billing Guidelines and Action Items 2026

The effective date on this modification is January 9, 2026. If your team is billing lymphocyte mitogen response assays, these are the steps to take now.

CPT, HCPCS, and ICD-10 Codes for Lymphocyte Mitogen Response Assays Under NCD 257

NCD 257 does not list specific CPT, HCPCS, or ICD-10 codes in the policy document. This is not unusual for older National Coverage Determinations — many NCDs predate the current code structure. But it does create a real problem for lymphocyte mitogen response assay billing.

No Specific Codes Listed in NCD 257

The absence of codes in the national policy means your Medicare Administrative Contractor is your best resource. MACs publish claims processing instructions that often map specific procedure codes to NCDs. Before billing lymphocyte mitogen response assays to Medicare, contact your MAC directly or review their LCD database for applicable codes.

Some labs have historically billed these assays under immunology panel codes or individual lymphocyte function test codes. Do not assume a code is correct because another provider uses it. Get written guidance from your MAC, document it in your billing files, and apply it consistently.

This is also a situation where your compliance officer should weigh in. Billing a test without confirmed code guidance creates upcoding and inappropriate billing risk — even when the clinical indication is clearly covered under the NCD. The covered indication and the correct code are two separate questions.