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CPC: ICD-10-CM Diagnosis Coding Across All Body Systems

CPC · Work through your exam, one topic at a time.

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ICD-10-CM Diagnosis Coding Across All Body Systems

This domain tests chapter-specific ICD-10-CM rules across the 21 chapters, with heavy emphasis on diabetes, circulatory disease, respiratory disease, neoplasms, injuries, pregnancy, and mental health. The exam expects you to apply combination codes, chapter notes, and external cause rules rather than memorize isolated codes.

Chapter rules that repeat

  • Diabetes E08-E13: combination codes capture manifestations; E11.9 is type 2 diabetes without complications; E11.22 requires an additional code for CKD stage; E11.65 is type 2 diabetes with hyperglycemia.
  • Circulatory: I10 is essential hypertension; I11.- is hypertensive heart disease; I13.- is hypertensive heart and chronic kidney disease. Do not add I10 when I11 or I13 is used. Myocardial infarction uses I21.- for the initial episode and I22.- for subsequent MI.
  • Respiratory: J44.1 is COPD with acute exacerbation; asthma codes from J45.- specify intermittent or persistent and exacerbation status. Code also tobacco use or dependence when documented.
  • Neoplasms: C00-C96 malignant, D00-D49 benign or uncertain behavior. The Table of Neoplasms identifies primary versus secondary sites; C80.1 is unspecified malignant neoplasm; Z85 is personal history of malignant neoplasm.
  • Injuries: S and T codes require a seventh character A, D, or S. External cause codes from V-Y identify cause, Y92 place of occurrence, and Y93 activity.
  • Pregnancy: Chapter 15 O codes require trimester and weeks of gestation; Z34 covers supervision of a normal pregnancy.
  • Mental health: F codes distinguish episodic and recurrent conditions and substance use with intoxication, dependence, or withdrawal.

Worked example

A patient has hypertensive heart disease with heart failure and stage 3a CKD. I13.0 covers hypertensive heart and CKD with heart failure and stage 1 through 4 CKD or unspecified CKD. Verify I13.0, then add N18.31 for stage 3a. Do not add I50.9 or I10; the combination code and stage code fully describe the encounter. If the CKD were stage 5 or ESRD, I13.2 would replace I13.0.

Traps

  • Coding both acute and chronic conditions unless the index or guidelines direct it.
  • Omitting external cause and place of occurrence for injuries.
  • Using C80.1 when the primary site is documented.
  • Assigning a trimester from the encounter date rather than the documented obstetric gestational age.
  • Confusing personal history Z codes with current-condition codes.