Coding Knowledge and Skills
Scope
This domain tests ICD-10-CM (diagnoses), ICD-10-PCS (inpatient procedures), CPT (outpatient procedures, E/M, radiology, laboratory, medicine) and HCPCS Level II (drugs, supplies, durable medical equipment). Expect questions on the official guideline hierarchy, the Alphabetic Index–to–Tabular List workflow, and the notations that control code combinations: code first, use additional code, code also, Excludes1 (two codes that may never appear together) and Excludes2 (two codes that may appear together when the conditions are distinct).
Concepts to know
Sequencing rules, the definition of principal diagnosis, seventh-character encounter types (initial, subsequent, sequela), laterality, combination codes, the surgical package, modifier use (e.g., 25 for a significant, separately identifiable E/M service; 59/X{EPSU} for distinct services), and the requirement to query the provider when documentation is ambiguous, incomplete, or contradictory.
Traps
Unspecified codes are valid when documentation truly lacks specificity, but questions usually reward the most specific code the record supports. Inpatient records may code “probable,” “suspected,” or “rule out” conditions as though established; outpatient coding requires provider confirmation. Another common trap is coding from a superbill, an order, or a lab result instead of the provider’s note.
Worked example
Documentation: “Acute cholecystitis with cholelithiasis, no obstruction.” Go to the Index under Cholecystitis → with cholelithiasis → acute, without obstruction, which leads to K80.00. That single combination code captures both the inflammation and the stones; do not add a separate calculus-of-gallbladder code. Always verify the entry in the Tabular List and read its Excludes notes before finalizing.