Can you explain the difference between ICD-10-CM, CPT, and HCPCS Level II coding systems, and when each is applied?

In medical coding, three major systems are used in the U.S. to capture diagnoses, procedures, services, and supplies. For students learning medical coding, it is essential to know which code set is used for what purpose, who maintains them, and when they are applied. Below is a guide to help you master these systems.

What each coding system is

1. ICD-10-CM (International Classification of Diseases, 10th Revision, Clinical Modification)

• Used for coding diagnoses, symptoms, conditions, and reasons for a patient’s visit (why care was sought).
• Developed by the Centers for Disease Control & Prevention (CDC) / National Center for Health Statistics (NCHS) in the U.S.
• Required under HIPAA for all health care providers when submitting claims.

2. CPT (Current Procedural Terminology)

• Managed by the American Medical Association (AMA).
• Used to code procedures and services performed by physicians and other health care professionals — for example surgeries, diagnostic tests, office visits, etc. (what was done).
• CPT is equivalent to HCPCS Level I.

3. HCPCS (Healthcare Common Procedure Coding System) Level II

• Maintained by the Centers for Medicare & Medicaid Services (CMS).
• Used for items, supplies, equipment, and certain services that are not covered by CPT codes. This includes durable medical equipment (DME), prosthetics, ambulance services, certain drugs, etc.
• Codes are alphanumeric (one letter + four digits) vs CPT which are 5 numeric digits.

When each is applied

Scenario Use ICD-10-CMUse CPT / HCPCS Level I Use HCPCS Level II Patient visits doctor for diagnosis and treatment The doctor documents the diagnosis → coder uses ICD-10-CM code. The services performed (exam, tests) → coded with CPT (HCPCS Level I).If the doctor uses supplies / durable medical equipment / devices during care outside what CPT describes → Level II codes.Inpatient hospital procedure (e.g. surgery within the hospital)Diagnoses still coded in ICD-10-CM.Not for inpatient facility procedures — those use ICD-10-PCS (another branch). CPT is often for professional services. If hospital uses devices or supplies not covered in CPT, HCPCS II may apply.Outpatient services, ambulance, prostheses, etc.Diagnoses using ICD-10-CM.The services (CPT).For supplies, ambulances, equipment not in CPT, to bill to insurance.

Some relevant statistics

• The U.S. medical coding market was estimated at USD 21.89 billion in 2024, and is expected to grow at a compound annual growth rate (CAGR) of about 10% from 2025 to 2033.
• Globally, the medical coding market size was about USD 38.58 billion in 2024, with projections to reach ~USD 89.49 billion by 2033.
• There is a ≈30% shortage of medical coders in the U.S., meaning many job openings and demand in this profession.
• Employment for medical records and health information specialists (which includes coders) is projected to grow about 7% from 2024 to 2034, which is faster than average for all occupations.

These stats show that knowing these coding systems is not just academic — it’s highly relevant for job prospects, efficiency of healthcare operations, and accurate billing / reimbursement.

Key differences in structure & maintenance

• ICD-10-CM: Updated annually. The code set includes modifications for specificity (laterality, injury, etc.).
• CPT (HCPCS Level I): Also updated annually by the AMA. Divided into sections such as Evaluation & Management, Surgery, Radiology, etc.
• HCPCS Level II: Maintained by CMS, updates multiple times per year especially for drugs/biologics and non-biologics items/services.

How I-Hub Talent can help Educational Students in Medical Coding

At I-Hub Talent, we understand that mastering these code sets is foundational for anyone pursuing a career in medical coding. Here’s how we support students

• Structured Curriculum: We offer modules that separately cover ICD-10-CM, CPT / HCPCS Level I, and HCPCS Level II, with real-world examples and practice exercises.
• Hands-on Coding Practice: Students get opportunity to code actual case studies, including outpatient, inpatient, services + supplies + equipment scenarios.
• Faculty Expertise: Our trainers have experience working with CMS, AMA, and in revenue cycle management; so they teach not just the rules but also how payers use these codes.
• Exam Prep & Certification Guidance: For certifications (e.g. AAPC, AHIMA), understanding these code sets deeply is mandatory — our course prepares students well.
• Job Readiness: Given the shortage of coders (~30%) and increasing market size, our courses aim to make students employable with resume assistance, mock interviews, and linkage with employers.

Conclusion

For students in a medical coding course, knowing the difference between ICD-10-CM (what was diagnosed), CPT / HCPCS Level I (what was done), and HCPCS Level II (what supplies, equipment, or non-CPT services were used) is essential. Each system is maintained by different agencies, updated on different schedules, and applied in different settings (inpatient vs outpatient, diagnosis vs procedure vs supplies). With the healthcare industry growing rapidly (CAGR ~10%), and a shortage of skilled professionals, proficiency in all three coding systems opens many career doors. At I-Hub Talent, we equip you with this proficiency through real case studies, expert instruction, and a curriculum aligned to what employers need. With these skills in hand, aren’t you ready to become a confident medical coder who can handle all three code sets?

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