They answer two different questions about the same visit.

ICD-10 (International Classification of Diseases, 10th revision) answers: what’s wrong with the patient? It codes diagnoses and conditions. Example: E11.9 = Type 2 diabetes without complications. Maintained by WHO; in the US we use ICD-10-CM (clinical modification) for diagnoses and ICD-10-PCS for inpatient procedures.
CPT (Current Procedural Terminology) answers: what did we do for the patient? It codes procedures, services, and encounters. Example: 99213 = established-patient outpatient visit, moderate complexity. Owned by the AMA.

Why both exist: billing and clinical analysis need both. To get paid, a claim says “we did procedure X (CPT) because the patient has diagnosis Y (ICD).” If the CPT doesn’t have a matching medically-necessary ICD, the claim gets denied.

Other related code sets to recognize:

HCPCS Level II — CMS’s procedure codes for things CPT doesn’t cover (durable medical equipment, ambulance, some drugs). Think of it as an extension to CPT for Medicare.
NDC (National Drug Code) — a specific prescribed drug, including manufacturer and strength.
LOINC — codes for lab results.
SNOMED CT — a richer clinical terminology increasingly used inside EHRs for problem lists, often mapped to ICD for reporting.

Common analyst gotchas:

ICD changes every October. New codes appear, old ones split. A multi-year query must handle code version transitions.
Diagnosis pointers. A claim can have multiple ICDs (primary + secondary + …); don’t collapse them without care.
CPT modifiers (-25, -59, -76) change meaning materially. A CPT without modifiers is an incomplete question.
ICD specificity varies. E11.9 (diabetes unspecified) vs E11.22 (diabetes with CKD) drive different HEDIS and HCC results.

What’s the difference between ICD-10 and CPT codes?

Draft your answer

Stuck? Peek at a hint

More healthcare questions