Medicare and Medicaid Covered Services

Medicare and Medicaid are the two largest public health insurance programs in the United States, collectively covering more than 160 million Americans (CMS, 2023 Enrollment Data). Each program operates under a distinct legal framework, serves a different population, and applies separate rules for what services qualify for reimbursement. Understanding the structural boundaries between covered, non-covered, and conditionally covered services is essential for patients, providers, and health administrators navigating federal and state reimbursement systems.

• Definition and scope
• Core mechanics or structure
• Causal relationships or drivers
• Classification boundaries
• Tradeoffs and tensions
• Common misconceptions
• Checklist or steps (non-advisory)
• Reference table or matrix
• References

Definition and scope

Medicare is a federal health insurance program established under Title XVIII of the Social Security Act (42 U.S.C. § 1395 et seq.). It covers individuals aged 65 and older, certain persons under 65 with qualifying disabilities, and individuals with End-Stage Renal Disease (ESRD) or Amyotrophic Lateral Sclerosis (ALS). As of 2023, Medicare enrollment stands at approximately 65.7 million beneficiaries (CMS Medicare Enrollment Dashboard).

Medicaid is a joint federal-state program established under Title XIX of the Social Security Act (42 U.S.C. § 1396 et seq.). It covers low-income individuals and families, pregnant women, children, elderly adults, and people with disabilities who meet income and categorical eligibility criteria. Because states administer Medicaid under federal guidelines, covered services vary across the 50 states and the District of Columbia. As of 2023, Medicaid enrollment reached approximately 94.5 million individuals (KFF State Health Facts, Medicaid Enrollment).

The scope of this reference covers both programs' mandatory and optional benefit structures, the statutory and regulatory sources that define covered services, and the programmatic distinctions that govern eligibility and reimbursement.

Core mechanics or structure

Medicare structure

Medicare is organized into four distinct parts, each governing a separate category of covered services:

• Part A (Hospital Insurance) covers inpatient hospital care, skilled nursing facility (SNF) care following a qualifying hospital stay of at least 3 consecutive days, hospice care, and limited home health care. Part A is premium-free for most beneficiaries who have paid Medicare taxes for at least 40 quarters (CMS Medicare Part A).
• Part B (Medical Insurance) covers outpatient services, physician visits, preventive care, durable medical equipment (DME), and certain home health services. The standard Part B premium was $174.70 per month in 2024 (CMS, 2024 Medicare Parts A & B Premiums and Deductibles).
• Part C (Medicare Advantage) allows beneficiaries to receive Medicare benefits through CMS-approved private health plans, which must cover at minimum all Part A and Part B services. Plans may offer supplemental benefits including dental, vision, and hearing.
• Part D (Prescription Drug Coverage) provides outpatient prescription drug benefits through private plan sponsors under contracts with CMS, governed by 42 C.F.R. Part 423.

Medicaid structure

Medicaid distinguishes between mandatory and optional services. States must cover all mandatory benefits to receive federal matching funds. Optional benefits may be added at state discretion.

Mandatory services (per 42 C.F.R. § 440) include inpatient and outpatient hospital services, physician services, laboratory and X-ray services, nursing facility services for adults, home health services, early and periodic screening, diagnostic, and treatment services (EPSDT) for individuals under 21, and family planning services.

Optional services include prescription drugs, dental care, vision services, physical and occupational therapy, prosthetics, and case management. As of 2024, all 50 states and D.C. cover prescription drugs as an optional benefit (KFF Medicaid Benefits).

Causal relationships or drivers

Three structural forces shape which services are covered under Medicare and Medicaid:

1. Statutory mandate and CMS rule-making
Congress defines covered service categories in Title XVIII and Title XIX; the Centers for Medicare & Medicaid Services (CMS) translates statutory language into operational coverage rules through the Code of Federal Regulations, National Coverage Determinations (NCDs), and Local Coverage Determinations (LCDs) issued by Medicare Administrative Contractors (MACs). An NCD establishes national policy; where no NCD exists, MACs may issue LCDs that vary by geographic region.

2. Actuarial and fiscal constraints
Benefit design in both programs reflects budget scoring by the Congressional Budget Office (CBO) and the CMS Office of the Actuary. Services enter covered status when their projected cost falls within appropriated funding levels or when evidence demonstrates that coverage reduces more expensive downstream utilization — a logic that explains, for example, the expansion of preventive health services and screenings under the Affordable Care Act (ACA) amendments to Medicare Part B.

3. Clinical evidence and technology assessment
Medicare's Coverage with Evidence Development (CED) pathway allows conditional coverage of promising technologies while requiring registries or trials to generate clinical evidence. The medical service accreditation and quality standards framework maintained by CMS and accreditation organizations such as The Joint Commission and NCQA also influences which service delivery models qualify for reimbursement.

Classification boundaries

Services fall into one of four operational classifications under Medicare and Medicaid:

Covered without conditions — Services explicitly listed as benefits that meet medical necessity criteria as defined under 42 C.F.R. § 411.15 and applicable NCDs/LCDs. Examples include inpatient hospitalization under Part A and physician evaluation and management (E/M) visits under Part B.

Covered with conditions (prior authorization or clinical criteria) — Services that require prior authorization, step therapy, or documented clinical necessity. Medicaid managed care plans may impose prior authorization requirements consistent with 42 C.F.R. § 438.210. Certain diagnostic and imaging services such as advanced MRI protocols fall here.

Statutorily excluded — Services explicitly excluded from Medicare coverage by 42 U.S.C. § 1395y(a), including routine dental care, routine vision and hearing exams, cosmetic surgery, custodial care not requiring skilled nursing, and most prescription drugs under Part A/B (addressed separately through Part D). Medicaid states may cover some of these as optional benefits.

Investigational and non-covered — Services classified as experimental or investigational that lack sufficient clinical evidence, identified through the Medicare Coverage Database maintained by CMS. CED applies to a subset.

The distinction between home health care services (covered under Medicare when skilled care is required and the patient is homebound) and custodial care (excluded) represents one of the most operationally significant classification boundaries in the program.

Tradeoffs and tensions

Federal uniformity vs. state flexibility
Medicare establishes national benefit standards with limited state variation. Medicaid's cooperative federal-state structure creates 51 distinct benefit packages, generating geographic inequities: a Medicaid beneficiary in one state may have access to dental services, behavioral health integration, and long-term services and supports that a beneficiary in another state does not.

Medical necessity definitions
Medicare's definition of medical necessity — that a service is "reasonable and necessary for the diagnosis or treatment of illness or injury" per 42 U.S.C. § 1395y(a)(1)(A) — creates recurring disputes between providers, beneficiaries, and MACs. Courts have interpreted this standard inconsistently, and the Administrative Law Judge (ALJ) appeals process under 42 C.F.R. Part 405 handles hundreds of thousands of coverage disputes annually.

Cost-sharing and equity
Medicare Part B requires a 20% coinsurance after the annual deductible ($240 in 2024, per CMS). Dual-eligible individuals (enrolled in both Medicare and Medicaid) may receive Low Income Subsidy (LIS) assistance, but navigating dual-eligibility coordination remains administratively complex, affecting access to mental health services in the US and other specialty services.

Benefit expansion pressures
The inclusion of telehealth and virtual medical services illustrates how external pressures — in this case, the COVID-19 public health emergency — drive rapid benefit expansion followed by contested policy decisions about permanent coverage. CMS extended many telehealth flexibilities through December 31, 2024 under the Consolidated Appropriations Act, 2023 (Pub. L. 117-328).

Common misconceptions

Misconception: Medicare covers long-term nursing home care indefinitely.
Medicare Part A covers skilled nursing facility care only following a qualifying inpatient hospital stay of at least 3 consecutive days, for up to 100 days per benefit period, with coinsurance applying after day 20. It does not cover custodial or long-term care. Medicaid, not Medicare, is the primary payer for long-term nursing facility services for individuals who have depleted assets to meet eligibility thresholds.

Misconception: Medicaid is only for unemployed individuals.
Medicaid eligibility is income-based, not employment-based. Working adults below 138% of the Federal Poverty Level in Medicaid expansion states may qualify. As of 2024, 41 states and D.C. have adopted the ACA Medicaid expansion (KFF State Medicaid Expansion Status).

Misconception: Medicare Advantage plans can deny any service.
Medicare Advantage plans must cover all services that Original Medicare covers. CMS finalized rules in the 2023 RADV Final Rule and the 2024 Medicare Advantage Rule (CMS-4201-F) limiting the use of prior authorization and requiring that coverage decisions align with Original Medicare criteria.

Misconception: Medicaid does not cover prescription drugs.
All 50 states and D.C. voluntarily cover outpatient prescription drugs as an optional benefit. Federal rebate requirements under 42 U.S.C. § 1396r-8 require drug manufacturers to pay rebates to state Medicaid programs, creating a national drug pricing mechanism within the optional benefit framework.

Misconception: Dental care is covered by Medicare.
Original Medicare (Parts A and B) does not cover routine dental services, examinations, or dentures. Limited dental coverage may be available through Medicare Advantage plans at plan discretion. Medicaid covers dental services in 30 states for adults as of 2024, with variation in scope (KFF Medicaid Adult Dental Benefits).

Checklist or steps (non-advisory)

The following sequence describes the structural process by which a service is evaluated for Medicare or Medicaid coverage. This is a reference framework, not procedural guidance.

1. Identify the program — Determine whether the service is being evaluated under Medicare (federal uniform rules) or Medicaid (state-specific plan rules under federal minimum standards).
2. Locate the applicable benefit category — Match the service type to a defined benefit category in 42 C.F.R. Part 409 (Part A), Part 410 (Part B), Part 422 (Part C), Part 423 (Part D), or 42 C.F.R. Part 440 (Medicaid).
3. Check for a National Coverage Determination (NCD) — Search the CMS Medicare Coverage Database at coverage.cms.gov for an existing NCD governing the service.
4. Check for a Local Coverage Determination (LCD) — If no NCD exists, identify the applicable MAC jurisdiction and review the corresponding LCD.
5. Review medical necessity criteria — Confirm whether the service meets the necessity definition under the applicable NCD, LCD, or state Medicaid coverage policy.
6. Assess prior authorization requirements — For Medicaid managed care or Medicare Advantage, determine whether prior authorization is required under the plan's evidence of coverage document.
7. Verify provider enrollment — Confirm the rendering provider is enrolled in Medicare or Medicaid and has active, unrevoked participation status via PECOS (Medicare Provider Enrollment).
8. Determine cost-sharing obligations — Identify applicable deductibles, coinsurance, or copayment amounts under the specific program and plan type.
9. Document dual-eligibility coordination if applicable — For dual-eligible individuals, determine which program is primary payer and apply Medicare Secondary Payer (MSP) rules under 42 C.F.R. Part 411.

Reference table or matrix

References

• Centers for Medicare & Medicaid Services (CMS) — Medicare Coverage Database
• [CMS — Medicare Parts A & B Premiums and Deductibles, 2024](https://www.cms.gov/newsroom/fact-sheets/2024-medicare-parts-b