STEP-BY-STEP CODING PROCESS:
  1. Identify the main term in the diagnosis
  2. Locate main term in ICD-10-CM Alphabetic Index
  3. Review subterms and notes under main term
  4. Follow cross-references (see, see also)
  5. Verify code in Tabular List (never code from index alone)
  6. Read all instructional notes in Tabular List
  7. Assign highest level of specificity
  8. Follow sequencing guidelines

MAIN TERMS IN INDEX:
  Condition: pneumonia, fracture, diabetes
  Eponyms: Crohn disease, Alzheimer disease
  Nouns: pain, infection, disorder
  NOT anatomy: never look up "knee" or "lung" — look up condition

PLACEHOLDER X:
  Used to fill character positions when code needs 7th character
  Example: S52.001A needs 7th char A, but only 6 chars used
  S52.001XA — X fills position 6 so A can be 7th

COMBINATION CODES:
  Single code that captures two conditions
  E11.65: Type 2 diabetes with hyperglycemia
  I25.110: Atherosclerotic heart disease with unstable angina
  Always use combination code when available

MULTIPLE CODING INSTRUCTIONS:
  Code first: underlying condition coded first
  Use additional code: secondary code must be added
  In diseases classified elsewhere: manifestation coded second

FRACTURES (S/T codes):
  7th characters:
    A = initial encounter, closed fracture
    B = initial encounter, open fracture (type I or II)
    D = subsequent, routine healing
    G = subsequent, delayed healing
    K = subsequent, nonunion
    S = sequela

BURNS (T20-T32):
  Code site and degree separately when multiple
  T31/T32: total body surface area (TBSA) for major burns
  Degrees: 1st (erythema), 2nd (blistering), 3rd (full thickness)

DIABETES COMPLICATIONS:
  Always link: diabetes + complication (causal relationship assumed)
  E11.21: Type 2 + diabetic nephropathy
  E11.311: Type 2 + unspecified diabetic retinopathy with macular edema
  E11.40: Type 2 + diabetic neuropathy, unspecified

SEPSIS:
  A41.9: Sepsis, unspecified (principal dx when reason for admission)
  Severe sepsis: A41.9 + R65.20 (without septic shock)
  Septic shock: A41.9 + R65.21 (always sequence sepsis first)
  Urosepsis: NOT a valid ICD-10-CM term — code underlying infection