How Medicare, Medicaid, and commercial payers “fit together” for outpatient primary care, and when reimbursement rules change.

This is operational context, not billing advice. Always verify your contract, payer policy, and current-year fee schedule.

See also: Coverage & Reimbursement Decisions for how medical necessity, prior auth, and claim edits drive what actually gets paid.

Shared foundations (most payers)#

• Coding language: most payers use CPT/HCPCS for services and ICD-10-CM for diagnoses.
• Documentation: medical necessity + payer-specific policy (coverage rules, prior auth, frequency limits).
• Adjudication: the payer converts your billed codes into an allowed amount, then applies patient cost-share (copay/coinsurance/deductible) and any edits/denials.

Medicare (traditional FFS)#

How reimbursement is determined#

• Physician Fee Schedule (PFS) for most outpatient E/M and procedures.
• Allowed amount is driven by the RVU system:
  • Code RVUs (wRVU/peRVU/mpRVU) × local GPCI × national conversion factor.
• Your clinic’s setting affects practice expense (facility vs non-facility).

When things change#

• Annually (main):
  • Proposed PFS rule (typically mid-year) → Final Rule (typically late fall) → effective Jan 1.
  • Updates include RVUs, covered services, documentation/coding policies, and the conversion factor.
• During the year (as needed):
  • Some policy edits and coverage decisions can change outside the annual cycle.
  • Local coverage policies can vary by MAC and may be updated throughout the year.

Medicaid (state-administered)#

How reimbursement is determined#

• Medicaid is run by states (within federal rules), so payment and policy vary widely.
• Many states base outpatient professional payment on some version of:
  • Medicare-derived fee schedules (often a percentage of Medicare), and/or
  • State-set rates for specific services.

When things change#

• State fee schedule updates: timing varies (often annual, sometimes mid-year).
• Managed care plans (if your Medicaid population is in MCOs): policies and rates may follow the plan’s contract and can change with contract amendments.

Commercial / private payers#

How reimbursement is determined#

Common patterns (depends on your contract):

• Percent of Medicare: allowed amount = some % of Medicare PFS (sometimes with modifiers by specialty, place of service, or code families).
• Fee schedule / case rates: payer-specific allowed amounts per code, negotiated directly.
• Value-based models: additional payments or withholds based on quality, utilization, and risk (e.g., PMPM, shared savings); E/M claims still matter for attribution and encounter capture.

When things change#

• Contract-driven: often on renewal/anniversary; sometimes tied to inflation indices or Medicare updates.
• Policy changes: medical policies, prior auth rules, and edits can change any time with payer notice.

How they relate (practical mental model)#

• Medicare is the reference point for many contracts and for the “language” of CPT/HCPCS + E/M rules.
• Medicaid often follows Medicare’s structure but is implemented and paid at the state/MCO level.
• Commercial payers frequently peg to Medicare (explicitly or implicitly) but vary the most in policy and contracting.

What to track in your practice (high-yield)#

• Your top 20 CPT/HCPCS codes and their payer mix (Medicare vs Medicaid vs commercial).
• For each payer:
  • Current fee schedule (or % of Medicare terms)
  • Key medical policies for common tests/procedures (labs, imaging, injections, procedures)
  • Prior auth and referral requirements
  • Common denial reasons and required documentation