5-DIGIT NUMERIC CODE: 10000-99499 (Category I)
  No letters in standard codes
  Organized by body system or specialty

ADD-ON CODES (+):
  Always reported with a primary code, never alone
  Example: 99292 (each additional 30 min critical care — add-on to 99291)
  Never append modifier -51 to add-on codes

MODIFIER 51 EXEMPT:
  Symbol: circle with slash
  Not subject to multiple procedure reduction
  Example: 93971 (duplex scan of extremity arteries, unilateral)

SEPARATE PROCEDURE:
  Parenthetical note "separate procedure"
  When integral to larger service, do not bill separately
  When performed alone, may be reported

INDEX LOOKUP:
  Main terms: procedure or service performed
    Appendectomy, colonoscopy, arthroplasty
  Body site: anatomical location
    Knee, shoulder, abdomen
  Condition: what is being treated
    Fracture, hernia, tumor
  Eponym: named procedures
    Whipple procedure, Mohs surgery

TABULAR SECTION:
  Always verify code in tabular after finding in index
  Read all instructional notes, parenthetical notes
  Check includes/excludes notes
  Verify all code options — index often lists only primary code

APPENDICES:
  Appendix A: complete modifier listing
  Appendix B: summary of additions/deletions/revisions
  Appendix C: clinical examples for E&M services
  Appendix D: summary of add-on codes

E&M (99202-99499): Most commonly billed codes
  New patient needs all 3 key components (or time/MDM)
  Established patient needs 2 of 3 key components
  2021 changes: time or MDM determines level (office/outpatient)

ANESTHESIA (00100-01999):
  Reported in units: base units + time units
  Physical status modifiers: P1 (normal) to P6 (brain dead)
  Qualifying circumstances: 99100-99140 (extreme age, emergency, etc.)

SURGERY (10004-69990):
  Includes local anesthesia, pre/post-op care in global package
  Report surgical service once even if bilateral (add -50)
  Unlisted codes end in -99 — requires special report attachment