Yes — Medicare Part B covers a cerebrospinal fluid (CSF) biomarker test for an Alzheimer's evaluation when a doctor orders it as medically necessary, and the lab portion usually costs you nothing. A CSF biomarker test measures amyloid and tau proteins in the clear fluid around the brain and spinal cord, drawn by lumbar puncture, to show whether Alzheimer's disease pathology is present. The catch is that two separate bills come out of one appointment. The laboratory analysis falls under Medicare's clinical lab benefit, while the spinal tap that collects the fluid is billed as a diagnostic procedure with its own coinsurance.
Medical information disclaimer: This article is for general educational purposes only and does not provide medical advice, diagnosis, or treatment. Always consult a physician or other qualified health professional about symptoms, medications, tests, or treatment decisions.
Official resources:
- Read the official notice from FDA — Use this primary source to verify the official announcement.
- Check eligibility on FDA’s official study page — Use this page to check the study’s participation requirements.
Table of Contents
- What the lab benefit actually pays
- The spinal tap is billed separately
- Why there is no single national rule
- The strongest reason a CSF test gets ordered — and paid
- What the test can and cannot tell you
- Steps to take before scheduling
- Frequently Asked Questions
What the lab benefit actually pays
Medicare Part B covers medically necessary clinical diagnostic laboratory tests ordered by a doctor or other treating provider. According to Medicare's page on diagnostic laboratory tests, beneficiaries generally pay nothing when the test is performed by a lab, pharmacy, doctor's office or hospital that accepts assignment. Medicare's 2026 cost figures list $0 for covered clinical laboratory services.
The 2026 Part B deductible is $283 per year, and it does not apply to the lab benefit itself. Medicare Advantage is a separate question. Medicare.gov directs Advantage members to check their own plan for out-of-pocket costs, because the plan sets cost sharing and network rules.
The spinal tap is billed separately
The lumbar puncture is not a lab test. It is a diagnostic non-laboratory service, and Medicare's rules for those are different: you pay 20% of the Medicare-approved amount after meeting the Part B deductible. If the procedure happens in a hospital outpatient department, a facility copayment may apply on top of the physician's charge.
That copayment is capped near the Part A deductible amount for the year. So a reader planning for this should expect a modest bill even when the analysis itself is free. Ask the ordering office whether the puncture will be done in a clinic or a hospital outpatient setting, because the setting drives the facility charge.
Why there is no single national rule
Medicare has no national coverage determination for CSF Alzheimer's biomarker testing. A Medicare Advantage policy covering the Lumipulse G β-Amyloid Ratio and Elecsys CSF assays states plainly that, with no NCD, local coverage determination or other guideline in place, the plan makes the coverage decision itself. Billing reinforces that patchwork.
These assays are reported with Proprietary Laboratory Analyses codes rather than a standard panel code — 0358U for the CSF β-amyloid 1-42/1-40 ratio by chemiluminescence immunoassay, and 0445U for CSF Abeta42/pTau181 by electrochemiluminescence, as set out in EmblemHealth's reimbursement policy on biochemical markers of Alzheimer disease. A proprietary code is tied to one manufacturer's test, so payment is set contractor by contractor. The practical consequence: coverage can differ between two patients in different states, or between Original Medicare and an Advantage plan in the same state. Documentation of medical necessity in the chart is what carries the claim.
The strongest reason a CSF test gets ordered — and paid
Anti-amyloid treatment changed the economics of this test. CMS National Coverage Determination 200.3, effective April 7, 2022, covers FDA-approved anti-amyloid monoclonal antibodies only for patients with a clinical diagnosis of mild cognitive impairment or mild Alzheimer's dementia, plus confirmed amyloid beta pathology. A CSF biomarker result is an accepted way to confirm that pathology.
The CMS registry for these drugs asks clinicians to submit the result of the patient's amyloid PET scan, CSF test, or other amyloid test, as described in the agency's fact sheet on covering the new Alzheimer's drugs. That makes the order easier to justify when treatment is genuinely on the table. If a patient is not a candidate for anti-amyloid therapy, the clinical rationale has to stand on its own.
What the test can and cannot tell you
The FDA authorized Fujirebio's Lumipulse G β-Amyloid Ratio (1-42/1-40) CSF test on May 4, 2022, as the first in vitro diagnostic for detecting amyloid plaques. The FDA's decision summary limits it to adults aged 55 and older who already have cognitive impairment, and states it is not a screening test and not a stand-alone diagnostic. That matters for expectations.
A positive result indicates amyloid pathology; it does not by itself name the cause of someone's symptoms, and it is not something to request in the absence of cognitive complaints. Real-world use is still narrow. Among 653,420 Medicare fee-for-service beneficiaries aged 67 and older newly diagnosed with MCI, Alzheimer's or another dementia between 2015 and 2020, only 2.2% had CSF testing in the year before diagnosis — 3.5% in the MCI group — compared with 53.9% who had neuroimaging, according to research published in Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring.
Steps to take before scheduling
A short checklist keeps the surprises down: There is now a less invasive route to the same question. On May 16, 2025 the FDA cleared the Lumipulse G pTau217/β-Amyloid 1-42 Plasma Ratio, the first blood test for amyloid plaques, for adults 55 and older with signs of Alzheimer's. It was cleared through the 510(k) pathway using the CSF ratio test as its predicate, so it is worth asking a neurologist whether a blood draw can answer the question before a spinal tap is scheduled.
- Confirm the ordering diagnosis and symptoms are documented, since medical necessity is the basis for the claim.
- Ask whether the performing laboratory accepts Medicare assignment, which is what produces the $0 lab cost.
- Ask which code the lab bills — 0358U or 0445U — and whether your contractor or Advantage plan has paid it before.
- For Medicare Advantage, request prior authorization in writing rather than assuming Original Medicare's rules apply.
- Budget for the lumbar puncture's 20% coinsurance and any hospital outpatient copayment.
Frequently Asked Questions
Does the Part B deductible apply to the CSF lab test?
Not to the laboratory analysis, which Medicare lists at $0 when performed under assignment. The $283 Part B deductible for 2026 does apply to the lumbar puncture, billed as a diagnostic non-laboratory service.
Can I ask for this test as a general Alzheimer's screening?
No. The FDA authorized the Lumipulse G CSF test for adults 55 and older who already present with cognitive impairment, and specified it is not a screening test.
Will Medicare Advantage cover it the same way?
Not automatically. With no national coverage determination in place, Advantage plans make the determination themselves, and Medicare directs Advantage members to their own plan for out-of-pocket costs.
