Medicare Eligibility Verification Guide 2026: Parts A, B, C,...

Medicare covers more than 67 million Americans, making it the single largest payer in the U.S. healthcare system. For most healthcare organizations -- particularly those serving older adults, patients with disabilities, or patients with end-stage renal disease -- Medicare represents a substantial portion of revenue.

Medicare eligibility verification is fundamentally different from commercial payer verification. The Medicare program is divided into four distinct parts (A, B, C, and D), each covering different services with different enrollment rules. A patient can have Original Medicare (Parts A and B), a Medicare Advantage plan (Part C) that replaces Original Medicare, a Part D prescription drug plan, a Medicare Supplement (Medigap) policy, or various combinations. On top of this, Medicare Secondary Payer (MSP) rules add coordination of benefits complexity that does not exist with most commercial payers.

Getting Medicare verification right requires understanding which parts of Medicare the patient has, whether Medicare is primary or secondary, and what specific coverage applies to the planned service. This guide covers the verification methods, part-by-part verification requirements, MSP rules, Medicare-specific pitfalls, and how AI handles Medicare's unique complexity.

Why Medicare Eligibility Verification Matters

Medicare eligibility errors create financial consequences that are uniquely difficult to recover.

Medicare conditional payment recovery. If Medicare pays a claim that should have been billed to another payer (because Medicare was secondary), CMS will recover that payment -- sometimes years later. Incorrect MSP determination during eligibility verification creates long-tail financial exposure.

Strict timely filing limits. Medicare has a 12-month timely filing deadline. If an eligibility error is discovered late, rebilling to the correct payer or coverage part may be impossible if the filing deadline has passed.

Part C (Medicare Advantage) complexity. Approximately 54% of Medicare beneficiaries are now enrolled in Medicare Advantage plans. These members have Medicare cards, but their claims go to the MA plan -- not to Original Medicare. Billing Original Medicare for an MA member results in a denial.

Compliance risk. Billing Medicare for services that are not covered, billing the patient for services that should be covered, or failing to identify MSP situations can create compliance exposure under the False Claims Act and other federal statutes.

ABN requirements. If a service may not be covered by Medicare, an Advance Beneficiary Notice (ABN) must be issued before the service is provided. Eligibility verification is the point at which non-covered services should be identified and ABN requirements triggered.

Understanding Medicare Parts A, B, C, and D

Before verifying Medicare eligibility, you need to understand what each part covers, because your verification must confirm enrollment in the relevant part for the service you plan to provide.

Part A: Hospital Insurance

Covers: Inpatient hospital stays, skilled nursing facility care, hospice care, and some home health services.

Enrollment: Most beneficiaries receive Part A automatically and premium-free when they turn 65 (if they or their spouse paid Medicare taxes for 40+ quarters). Others can buy into Part A by paying a premium.

Verification importance: Confirm Part A enrollment and effective date. Also verify whether the patient has a Part A deductible remaining (the Part A inpatient deductible resets per benefit period, not per calendar year).

Part B: Medical Insurance

Covers: Physician services, outpatient care, preventive services, durable medical equipment, ambulance services, mental health services, and many other outpatient services.

Enrollment: Part B requires active enrollment and a monthly premium. Not all Medicare beneficiaries have Part B -- some delay enrollment or opt out.

Verification importance: Many services billed by physician practices and outpatient facilities fall under Part B. Confirming Part B enrollment is essential. Also verify whether the Part B deductible has been met for the calendar year.

Part C: Medicare Advantage

Covers: Everything covered by Parts A and B, often with additional benefits (dental, vision, hearing, fitness), but through a private insurance plan rather than Original Medicare.

Enrollment: Beneficiaries choose to enroll in an MA plan during specific enrollment periods. They still have Medicare, but their coverage is administered by the MA plan.

Verification importance: MA members must be verified and billed through their MA plan, not through Original Medicare. The MA plan may have its own network requirements, prior authorization rules, and cost-sharing structures.

Part D: Prescription Drug Coverage

Covers: Outpatient prescription drugs.

Enrollment: Part D is offered through standalone Prescription Drug Plans (PDPs) or as part of Medicare Advantage plans that include drug coverage (MA-PD).

Verification importance: Primarily relevant for pharmacy claims, but also important for practices that administer drugs (physician-administered Part B drugs vs. self-administered Part D drugs).

Methods to Verify Medicare Eligibility

HETS (HIPAA Eligibility Transaction System)

HETS is CMS's system for processing electronic eligibility inquiries for Original Medicare (Parts A and B). It is the primary and most reliable method for verifying Original Medicare enrollment.

How HETS works:

Your clearinghouse or practice management system submits a 270 eligibility inquiry to CMS through HETS
CMS returns a 271 response with the beneficiary's Medicare enrollment status, including Part A and Part B effective dates, deductible information, and MSP data
The response is parsed and integrated into your patient record

What HETS provides:

Part A enrollment status and effective date
Part B enrollment status and effective date
Part A deductible information (benefit period deductible)
Part B deductible information (calendar year deductible)
Medicare Advantage enrollment indicator (if the beneficiary is in an MA plan, HETS will indicate this and provide the MA plan information)
Medicare Secondary Payer (MSP) information
Hospice status
Medicare entitlement reason (age, disability, ESRD)

HETS limitations:

HETS verifies Original Medicare (Parts A and B) enrollment. For beneficiaries enrolled in Medicare Advantage, HETS will indicate MA enrollment but will not provide the MA plan's specific benefits or cost-sharing details. You must verify those directly with the MA plan.
HETS does not provide Part D (prescription drug) eligibility information.

Medicare Administrative Contractor (MAC) Portals

Each MAC (the contractors that process Medicare claims for specific regions) offers a provider portal with eligibility verification capabilities.

Common MAC portals:

Novitas Solutions: Jurisdiction JH and JL
First Coast Service Options: Jurisdiction JN
CGS Administrators: Jurisdiction 15
NGS (National Government Services): Jurisdiction JK and J6
Palmetto GBA: Jurisdiction JJ and JM
WPS Government Health Administrators: Jurisdiction J5 and J8

What MAC portals provide:

Medicare eligibility and enrollment status
Claims history and status
Deductible and coinsurance information
MSP information
Prior authorization status (for services requiring Medicare prior auth)

When to use MAC portals: MAC portals are useful for detailed Medicare-specific inquiries that go beyond what the standard 271 response provides, such as benefit period tracking, MSP detail, and claims history review.

Medicare Advantage Plan Portals

For beneficiaries enrolled in Medicare Advantage, you must verify specific benefits, cost-sharing, and authorization requirements through the MA plan's provider portal -- not through HETS or the MAC.

Major MA plan portals:

UnitedHealthcare Medicare & Retirement: UHCProvider.com
Humana: Availity or Humana's provider portal
CVS Health/Aetna Medicare: Availity or Aetna's provider portal
Cigna Medicare: CignaforHCP.com
Blue Cross Blue Shield MA plans: Varies by BCBS licensee

Each MA plan has its own network, authorization requirements, and benefit design. Verifying through the plan-specific portal ensures you receive accurate benefit information for the member's specific MA plan.

CMS PECOS (Provider Enrollment, Chain, and Ownership System)

While not an eligibility verification tool, PECOS is relevant because providers must be enrolled in Medicare to bill Medicare. If your practice has a new provider or a provider whose Medicare enrollment has lapsed, eligibility verification will succeed (the patient has coverage) but the claim will deny (the provider cannot bill Medicare).

Phone Verification

For complex Medicare eligibility questions, direct phone verification is available.

Medicare Provider Services: 1-800-MEDICARE (1-800-633-4227) -- automated system with provider option

Medicare Administrative Contractor phone lines: Each MAC has a dedicated provider inquiry line. The number varies by jurisdiction and is available on the MAC's website.

When to use phone verification:

MSP situations that need clarification
Benefit period questions (Part A)
Entitlement end dates (disability beneficiaries returning to work)
Hospice status questions
ESRD coordination periods
Retroactive eligibility changes

What to Verify Beyond Active Coverage

Part-Specific Enrollment

Verify enrollment in the specific Medicare part that covers the service you plan to provide:

Outpatient physician services: Part B enrollment required
Inpatient hospital admission: Part A enrollment required
Outpatient hospital services: Part B enrollment required
Skilled nursing facility: Part A enrollment required
Home health: Part A or Part B depending on the service
Durable medical equipment: Part B enrollment required

Do not assume that a patient with Part A also has Part B, or vice versa. Some beneficiaries have Part A only (premium-free) and have not enrolled in Part B.

Medicare Advantage Enrollment

If the patient is enrolled in a Medicare Advantage plan, the HETS response will indicate MA enrollment. You must then:

Identify the specific MA plan
Verify benefits, cost-sharing, and authorization requirements through the MA plan
Submit claims to the MA plan, not to Original Medicare

The most common Medicare eligibility error is billing Original Medicare for a Medicare Advantage member. This results in a denial and a delayed payment cycle as the claim is redirected to the MA plan.

Medicare Secondary Payer (MSP) Determination

MSP rules determine when Medicare is the secondary payer -- meaning another insurer is primary and must be billed first. MSP situations include:

Working aged: The beneficiary (or their spouse) is actively employed and has employer group health plan coverage. If the employer has 20+ employees, the employer plan is primary and Medicare is secondary.
Disability and large group health plan (LGHP): The beneficiary is under 65, eligible for Medicare due to disability, and has LGHP coverage through their own or a family member's employment with an employer of 100+ employees. The LGHP is primary.
End-stage renal disease (ESRD): During the first 30 months of ESRD-based Medicare eligibility, the beneficiary's employer group health plan is typically primary. After the coordination period, Medicare becomes primary.
Workers' compensation: If the service is related to a work injury, workers' compensation is primary.
Auto insurance / liability: If the service is related to an accident covered by auto or liability insurance, that insurer is primary.
Veterans Affairs: VA benefits do not create an MSP situation (Medicare does not pay secondary to VA), but services covered by VA should not be billed to Medicare.

Why MSP verification matters: If you bill Medicare as primary when another payer is primary, Medicare will initially pay the claim but will later identify the MSP situation and demand repayment -- potentially with interest. MSP recoveries can occur years after the original payment.

Deductible and Coinsurance Status

Part A inpatient deductible: Resets per benefit period (not per calendar year). The 2026 Part A deductible applies to each benefit period. Verify whether the patient is in an active benefit period and whether the deductible has been met.

Part B deductible: An annual deductible that resets each January 1. Verify whether the Part B deductible has been met for the current calendar year.

Part B coinsurance: After the deductible, Medicare pays 80% and the beneficiary is responsible for 20% coinsurance (unless they have supplemental coverage). Verify whether a Medigap or other supplemental policy covers this coinsurance.

Medigap (Medicare Supplement) Coverage

Many Original Medicare beneficiaries carry a Medigap policy that covers some or all of the cost-sharing (deductibles, coinsurance) that Original Medicare does not pay. If the patient has Medigap:

Bill Original Medicare first
The Medigap plan covers the remaining patient responsibility based on the Medigap plan type (A through N)
Many Medigap claims cross over automatically from Medicare to the supplement

Identifying Medigap coverage during eligibility verification prevents incorrect patient billing and improves collection efficiency.

Common Medicare Eligibility Pitfalls

Billing Original Medicare for Medicare Advantage Members

This is the most frequent and most costly Medicare eligibility error. Over half of Medicare beneficiaries are now in MA plans. Their Medicare card may show a Medicare Beneficiary Identifier (MBI), but their claims must go to the MA plan.

How to catch it: HETS will indicate MA enrollment. Your verification process must flag MA members and route them to the correct MA plan verification and billing pathway.

Missing MSP Situations

MSP is one of the most complex areas of Medicare billing. Common MSP errors include:

Not asking working-age patients (65+) whether they have employer coverage
Not identifying ESRD coordination periods
Not checking for liability or workers' compensation primary coverage

How to catch it: Implement systematic MSP screening at registration. Use the MSP questionnaire for all Medicare beneficiaries, not just those who volunteer information about other coverage. HETS responses include MSP data, but the data is only as accurate as what CMS has on file. Direct patient inquiry is still necessary.

Part A Without Part B

Some beneficiaries have Part A only (premium-free through work history) and have not enrolled in Part B. If you provide an outpatient service that requires Part B coverage and the patient does not have Part B, the service is not covered by Medicare.

How to catch it: Always verify both Part A and Part B enrollment. If the patient lacks Part B, determine whether the service is covered under Part A or whether the patient must pay out of pocket. Issue an ABN if appropriate.

Benefit Period Confusion (Part A)

Medicare Part A uses a benefit period structure rather than a calendar year structure for inpatient services. A benefit period begins when the patient is admitted and ends when the patient has not received inpatient or skilled nursing care for 60 consecutive days. The Part A deductible applies per benefit period, and benefit periods can span calendar years.

Common error: Assuming the Part A deductible resets on January 1 (it does not -- it resets when a new benefit period begins).

ABN Failures

When a service may not be covered by Medicare (either because it is excluded from Medicare coverage or because it may not meet medical necessity criteria), an ABN must be issued to the patient before the service is provided. Without a valid ABN, the provider cannot bill the patient for the non-covered service.

How to catch it: During eligibility verification, identify services that may not be covered and trigger the ABN workflow before the patient proceeds.

ESRD Coordination Period Errors

Patients with ESRD-based Medicare eligibility have a 30-month coordination period during which their employer group health plan (if they have one) is primary and Medicare is secondary. After the coordination period, Medicare becomes primary.

Common error: Billing Medicare as primary during the coordination period, or billing the employer plan as primary after the coordination period has ended.

Hospice Overlay

When a Medicare beneficiary elects hospice (Part A benefit), Medicare coverage for services related to the terminal illness is provided through the hospice benefit. Services unrelated to the terminal illness are still covered under regular Medicare. However, if a service is related to the hospice diagnosis and the provider bills regular Medicare instead of coordinating with the hospice, the claim will deny.

How to catch it: HETS responses include a hospice indicator. When a patient is identified as being on hospice, coordinate with the hospice provider to determine whether the planned service is related to the terminal diagnosis.

How AI Automates Medicare Eligibility Verification

Medicare's multi-part structure, MSP rules, MA plan variation, and benefit period tracking make manual verification especially burdensome and error-prone. AI-powered verification addresses each of these challenges.

Automated Part Detection

AI verifies enrollment in all applicable Medicare parts (A, B, C, D) in a single automated process. When MA enrollment is detected, the system automatically routes verification to the specific MA plan for benefit and authorization details.

MSP Screening and Detection

AI cross-references HETS MSP data with patient registration information to identify MSP situations. The system flags cases where another payer may be primary -- working-aged beneficiaries with employer coverage, ESRD coordination period patients, and liability/workers' compensation situations -- and routes them for appropriate primary payer billing.

Benefit Period Tracking

For Part A services, AI tracks benefit period status, including whether the patient is in an active benefit period, the deductible status within the current benefit period, and coinsurance day counts for extended stays.

MA Plan-Specific Verification

When a beneficiary is enrolled in a Medicare Advantage plan, AI verifies benefits, cost-sharing, network status, and authorization requirements through the MA plan's specific channels -- not through Original Medicare. This prevents the most common Medicare billing error.

ABN Trigger Identification

AI identifies services that may not meet Medicare coverage criteria and triggers the ABN workflow before the service is provided. This protects the organization's ability to bill the patient for non-covered services.

Medigap and Supplemental Detection

AI identifies Medigap and other supplemental coverage during verification, determining whether crossover claims will process automatically or need manual secondary billing.

ESRD Coordination Period Management

AI tracks ESRD coordination period timelines, automatically determining whether the employer plan or Medicare is primary based on the patient's coordination period status.

Hospice Overlay Awareness

When HETS indicates hospice status, AI flags the planned service for coordination with the hospice provider to determine whether it is related to the terminal diagnosis.

Building a Medicare Verification Workflow

Registration/Scheduling: Capture Medicare Beneficiary Identifier (MBI), run HETS inquiry, administer MSP screening questionnaire
Part and plan detection: Confirm Parts A and B enrollment, identify MA enrollment (route to MA plan if applicable), identify supplemental/Medigap coverage
MSP determination: Determine whether Medicare is primary or secondary based on HETS data and patient responses
Benefit verification: Verify specific service coverage under the applicable Medicare part or MA plan, check authorization requirements
Deductible and coinsurance: Verify deductible status and cost-sharing, generate patient cost estimate
ABN workflow: Issue ABN for potentially non-covered services before the service is provided
Day of service: Final verification, confirm no coverage changes, collect patient responsibility
Post-service: Ensure claims are routed to the correct entity (MAC for Original Medicare, MA plan for Part C) with correct MSP indicators

Internal Link References:

QuickIntell's QuickAuth performs real-time Medicare eligibility verification across Original Medicare (Parts A and B), all Medicare Advantage plans, Medigap policies, and Part D plans. It automates MSP determination, tracks benefit periods, identifies ABN requirements, and routes claims to the correct billing entity. See how QuickAuth works for your Medicare patient population.