Coding and Classification Systems
What the candidate must know
Understand the purpose and structure of the major code sets and how they interoperate. Know that ICD-10-CM classifies diagnoses (injury codes, external cause codes, Z codes for factors influencing health status), while ICD-10-PCS classifies inpatient procedures using seven characters: section, body system, root operation, body part, approach, device, qualifier. CPT describes outpatient/physician services and is divided into Category I (five-digit procedure codes), Category II (performance measurement, four digits plus F), and Category III (emerging technology, four digits plus T). HCPCS Level II covers supplies, drugs, and equipment not represented in CPT.
Traps in questions
- Confusing PCS root operations (e.g., Excision vs. Resection, Drainage vs. Extirpation) - read the definition, not the everyday meaning.
- Mixing outpatient procedure coding (CPT/HCPCS) with inpatient procedure coding (PCS). Setting drives the code set.
- Assuming a code set is updated only annually; ICD-10-CM/PCS and CPT have different update cycles.
- Forgetting that external cause and status codes are supplementary and never principal.
Rule of thumb
Let the care setting and the type of service pick the code set: diagnoses always ICD-10-CM; inpatient procedures always ICD-10-PCS; outpatient procedures and physician services CPT/HCPCS.
Worked example: An inpatient has a laparoscopic removal of the gallbladder. Because it is inpatient, code the procedure in ICD-10-PCS (section 0, body system F, root operation Resection, approach percutaneous endoscopic), not CPT.