Every claim answers three questions: what was wrong with the patient, what was done and what was supplied. Different code sets answer each one.
ICD-10-CM: the diagnosis
ICD-10-CM codes describe the patient's diagnoses, symptoms and conditions, and explain why a service was needed. The code set is updated each year, with changes taking effect on October 1.
CPT: the service performed
CPT (Current Procedural Terminology) codes describe the services and procedures providers perform, including office visits, tests and surgery. They are maintained by the American Medical Association and updated each year, with most changes effective January 1. Since 2021, office and outpatient visit levels are chosen based on medical decision-making or total time.
HCPCS Level II: supplies and other services
HCPCS Level II codes are maintained by CMS. They cover items and services outside CPT, including many drugs, supplies, ambulance services and durable medical equipment. They are updated quarterly.
How they work together
A claim links diagnosis codes to the procedure codes they support. If the diagnosis does not justify the procedure, the payer may deny it as not medically necessary or as inconsistent. Modifiers then add detail to the procedure code.
Why accurate coding matters
Codes drive payment, and they also create compliance risk. Under-coding leaves money behind, and over-coding can trigger audits and repayment demands. Coding has to follow the documentation, not the other way around. Our certified coders handle this as part of our medical coding services.
Frequently Asked Questions
Who maintains CPT codes?
The American Medical Association.
How often do code sets change?
ICD-10-CM updates take effect each October, CPT each January, and HCPCS Level II updates are issued quarterly.
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