Residency · Residency · Preventive Medicine

Structure of the U.S. Healthcare System

Overview

The U.S. healthcare system is a complex mixture of public and private financing and delivery mechanisms. There is no single national health system; instead, a patchwork of programs, insurers, and providers covers the population in overlapping and sometimes inconsistent ways. The U.S. spends more per capita on healthcare than any other nation — approximately $4.5 trillion annually, representing about 18% of GDP — yet produces worse outcomes on many population health metrics compared to peer countries. Understanding this system's structure is essential for preventive medicine physicians who work across clinical, administrative, and policy roles.

Health Insurance Coverage Landscape

Employer-Sponsored Insurance (ESI)

Employer-sponsored insurance covers approximately 49% of the U.S. population, making it the dominant source of coverage. Employers typically share premium costs with employees. The Employee Retirement Income Security Act (ERISA) of 1974 preempts state regulation of self-insured employer plans, creating a divided regulatory landscape between self-insured plans (common among large employers) and fully insured plans (purchased from commercial insurers by smaller employers). The tax exclusion of employer-sponsored health benefits represents the largest health-related tax expenditure in the federal budget.

Medicare

Medicare is a federal program serving adults aged 65 and older, individuals with end-stage renal disease, and certain disabled persons, covering approximately 65 million beneficiaries. Part A provides hospital insurance covering inpatient care, skilled nursing facility care, and hospice, funded primarily through payroll taxes. Part B provides medical insurance for outpatient services, physician visits, and preventive services, funded by beneficiary premiums and general revenue. Part C, known as Medicare Advantage, consists of private managed care plans that contract with CMS to deliver Part A and B benefits; approximately 50% of beneficiaries are now enrolled in these plans. Part D provides prescription drug coverage through private plans, featuring a coverage gap (the "donut hole") that is narrowing under provisions of the Inflation Reduction Act. The Centers for Medicare and Medicaid Services (CMS) administers the program.

Medicaid

Medicaid is a joint federal-state program for low-income individuals and families, covering approximately 90 million enrollees and representing the largest single source of health coverage in the United States. The federal government sets minimum requirements, but states have significant flexibility in determining eligibility criteria, benefit packages, and provider payment rates. The ACA Medicaid expansion extended eligibility to adults with incomes up to 138% of the federal poverty level, adopted by 40 states plus the District of Columbia as of 2024. Managed care delivery predominates, with approximately 80% of Medicaid beneficiaries enrolled in managed care plans. The Children's Health Insurance Program (CHIP) covers children in families with incomes too high for Medicaid but too low for affordable private insurance.

Individual/Marketplace Insurance

The ACA established Health Insurance Marketplaces — both federal and state-based exchanges — where individuals can purchase coverage. Premium tax credits are available for those with incomes between 100% and 400% of the federal poverty level, expanded under the American Rescue Plan and Inflation Reduction Act through 2025. All marketplace plans must cover ten categories of essential health benefits, including preventive services. The individual mandate penalty was eliminated at the federal level in 2019, though some states retain their own mandates.

Uninsured Population

Approximately 25-27 million Americans remain uninsured. A coverage gap exists in non-expansion states where adults with incomes below 100% FPL earn too much for traditional Medicaid but too little to qualify for marketplace subsidies. The uninsured disproportionately include Hispanic/Latino populations, young adults, and non-citizens. Uninsured individuals experience delayed care, worse health outcomes, and rely disproportionately on emergency departments for what should be primary care services.

Veterans Health Administration (VA)

The VA operates the largest integrated healthcare system in the United States, serving approximately 9 million enrolled veterans. It directly provides care through VA medical centers and community-based outpatient clinics. The VA has been a leader in electronic health record adoption, quality measurement, and population health management. TRICARE, a separate program administered by the Defense Health Agency (DHA), serves active-duty military, retirees, and their dependents.

Indian Health Service (IHS)

The Indian Health Service fulfills the federal government's obligation to provide healthcare to American Indian and Alaska Native populations. It is chronically underfunded relative to the health needs of the populations it serves. The IHS operates hospitals and clinics on or near reservations and also contracts with tribal organizations and urban Indian health programs.

Healthcare Delivery Models

Fee-for-Service (FFS)

The traditional fee-for-service model pays providers for each service rendered. This creates incentives favoring volume over value, and is associated with overutilization, care fragmentation, and higher costs. Despite reform efforts, fee-for-service remains predominant in many settings, particularly specialty care.

Managed Care

Health Maintenance Organizations (HMOs) use capitated payment with a gatekeeper model and restricted provider networks. Preferred Provider Organizations (PPOs) offer broader networks but apply higher cost-sharing for out-of-network care. Point of Service (POS) plans combine features of both models. Managed care organizations employ tools such as utilization review, prior authorization, and formulary management to control costs and coordinate care.

Integrated Delivery Systems

Integrated systems combine insurance and provider functions within a single organization, as exemplified by Kaiser Permanente. This alignment of incentives promotes prevention, care coordination, and cost control. Accountable Care Organizations (ACOs) represent a newer model in which groups of providers share responsibility for both the quality and cost of care for a defined patient population.

Community Health Centers (FQHCs)

Federally Qualified Health Centers serve medically underserved populations regardless of ability to pay, using a sliding fee scale based on income. Approximately 1,400 health center organizations operate through roughly 15,000 delivery sites nationwide. They provide primary care, dental services, behavioral health, and pharmacy services. FQHCs serve as the critical safety net for uninsured and Medicaid populations.

Key Federal Agencies and Regulatory Bodies

Department of Health and Human Services (HHS)

HHS serves as the umbrella agency for most federal health programs. Key operating divisions include CMS (Medicare, Medicaid, CHIP, and marketplace oversight), the CDC (public health surveillance, prevention, and emergency response), the FDA (drug, device, and food safety regulation), NIH (biomedical research funding), HRSA (safety net programs, workforce development, and maternal-child health), SAMHSA (substance use and mental health services), AHRQ (healthcare quality and patient safety research), and IHS (healthcare for American Indian and Alaska Native populations).

State and Local Health Departments

State and local health departments bear primary responsibility for population health at the community level. Their functions include disease surveillance, vital statistics registration, environmental health protection, maternal-child health programs, and emergency preparedness. They are funded through a combination of federal grants, state appropriations, and fees, with significant variation in structure and capacity across jurisdictions.

Healthcare Costs and Spending

Drivers of Healthcare Spending

Prices rather than utilization are the primary driver of high U.S. spending compared to other nations. Administrative costs account for approximately 34% of total healthcare expenditure. Additional cost drivers include pharmaceutical spending, specialist-driven care patterns, defensive medicine, and intensive end-of-life care. Technology is frequently adopted without rigorous cost-effectiveness evaluation.

Payment Reform Efforts

The ongoing shift from volume-based to value-based payment includes initiatives such as MACRA/MIPS, bundled payments, ACOs, and global budgets. Maryland's all-payer rate setting model represents one approach. Reference pricing, site-neutral payment policies, and drug price negotiation provisions under the Inflation Reduction Act represent additional reform mechanisms.

<image>A diagram of the U.S. healthcare coverage landscape showing the major sources of insurance coverage as a stacked population chart. Segments include employer-sponsored insurance (~49%), Medicaid/CHIP (~27%), Medicare (~19%), individual/marketplace (~6%), VA/military (~3%), and uninsured (~8%), with approximate population numbers. Arrows show the flow of funding from payroll taxes, general revenue, premiums, and out-of-pocket spending. Clean infographic style suitable for health policy education.</image>

<image>An organizational chart of the Department of Health and Human Services (HHS) showing its major operating divisions including CMS, CDC, FDA, NIH, HRSA, SAMHSA, AHRQ, and IHS. Each division has a brief annotation describing its primary function. The chart shows hierarchical reporting to the HHS Secretary. Clean government organizational chart style for medical education.</image>

<image>A comparison infographic showing U.S. healthcare spending per capita versus other high-income countries (Canada, UK, Germany, France, Japan, Australia) alongside key health outcome metrics (life expectancy, infant mortality, maternal mortality). The U.S. shows highest spending but worse outcomes on most metrics. Bar charts for spending and outcome indicators side by side. Health policy education illustration.</image>

Clinical Pearls

The employer-sponsored insurance tax exclusion is regressive — it benefits higher-income employees disproportionately and constitutes the single largest federal health-related tax expenditure. Medicaid is the single largest payer for births, long-term care, and behavioral health services in the United States. The coverage gap in non-expansion states affects approximately 2 million adults who have no affordable insurance option available to them. Medicare Advantage enrollment has surpassed 50% of Medicare beneficiaries, fundamentally changing how the program is delivered. FQHCs are the backbone of the healthcare safety net, and understanding their role is critical for any preventive medicine physician working with underserved populations. For board preparation, know the parts of Medicare (A, B, C, D), the difference between Medicaid and Medicare, and the roles of key federal agencies.

References

• Oberlander J. The political life of Medicare. University of Chicago Press; 2003.
• Starr P. The Social Transformation of American Medicine. Basic Books; 1982.
• Kaiser Family Foundation. Health Insurance Coverage of the Total Population. KFF; 2024.
• CMS. National Health Expenditure Data. cms.gov; 2024.
• Papanicolas I, et al. Health care spending in the United States and other high-income countries. JAMA. 2018;319(10):1024-1039.
• Sommers BD, et al. Changes in utilization and health among ACA Medicaid expansion enrollees. JAMA Intern Med. 2016;176(10):1470-1479.

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