Medicare does not automatically cover an amyloid beta 42/40 blood test for an Alzheimer's evaluation. Coverage depends on symptoms, the exact test ordered, and decisions by the regional Medicare contractor. The test measures the ratio of two amyloid protein fragments in plasma, and a low ratio can signal brain amyloid buildup tied to Alzheimer's disease.
As of November 2026, Medicare had no national coverage rule for Alzheimer's plasma biomarker tests, HealthcareOnTime reported in its November 2026 coverage update. That leaves payment to vary by lab, test, and contractor. Screening without symptoms is not covered.
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:
- Check eligibility on CMS’s official study page — Use this page to check the study’s participation requirements.
- Read the official guidance from CMS — Use this primary source to verify the official guidance.
Table of Contents
- What does this blood test measure?
- Why is there no simple yes-or-no answer?
- When is coverage more likely?
- What should you confirm before the blood draw?
What does this blood test measure?
The amyloid beta 42/40 ratio compares a sticky 42-amino-acid fragment with a more abundant 40-amino-acid fragment. A lower ratio suggests amyloid plaques may be present in the brain. It is a risk signal, not proof of dementia cause on its own. One cleared option combines that ratio with a tau marker.
Practical Neurology reported FDA clearance on August 20, 2026 for symptomatic adults 40 and older in its clearance report for PrecivityAD2. The test uses mass spectrometry to measure Aβ42/40 and percent p-tau217, then produces an amyloid-probability score. Cleared blood tests are adjuncts, not standalone diagnoses or population screens. Results need interpretation with a clinical workup by a clinician experienced in cognitive impairment. Normal cognition, other brain disorders, and mixed causes can still require further testing.
Why is there no simple yes-or-no answer?
Medicare uses national rules for some services and local rules for others. Plasma Alzheimer biomarkers fall in the local group, so contractors decide what is reasonable and necessary. Test brand, diagnosis codes, and notes on cognitive symptoms all matter. A prior national limit on amyloid PET scans ended in October 2023.
Local contractors now make those decisions too, with no broad amyloid-specific local rule in place. Blood tests face a similar patchwork, not one Medicare-wide policy. Many Medicare Advantage and commercial plans still label plasma Alzheimer biomarkers as investigational. Symptomatic patients can therefore face approval in one plan and denial in another. A written pre-test coverage check avoids surprise bills.
When is coverage more likely?
Medical need drives the decision. Evaluation for memory loss, confusion, or functional decline carries more weight than testing from curiosity or family history alone. The order should tie the test to an Alzheimer's evaluation in the medical record. Treatment planning is another pathway.
CMS covers FDA-approved anti-amyloid antibodies only for mild cognitive impairment or mild dementia with confirmed amyloid pathology and physician participation in a CMS registry study. The CMS registry study description expressly lists blood tests alongside PET and spinal-fluid studies as acceptable confirmation in its registry study description. That registry language does not make every evaluation test automatically payable. It helps most when the patient fits the treatment-eligibility track and the doctor documents each element:.
- mild cognitive impairment or mild dementia linked to possible Alzheimer's
- need to confirm amyloid before treatment decisions
- use of a validated amyloid blood test for that purpose
- physician participation in the required CMS registry process
What should you confirm before the blood draw?
Ask the ordering clinic for a specific coverage determination for the exact test name. Get the CPT code, the diagnosis code, and whether prior authorization is required. Ask what you would owe if Medicare denies the claim. Choose a clinic used to cognitive evaluation.
Bring a medication list, symptom timeline, and a family member who has seen day-to-day changes. Ask how a positive, negative, or borderline result would change next steps such as PET, spinal-fluid testing, referral, or treatment planning. Get the lab plan in writing, including sample handling and turnaround time. If coverage is uncertain, ask for the cash price and payment options before the needle stick. Do not schedule the test as annual screening and expect Medicare to pay.
