The Difference Between ICD-10-CM, CPT, and HCPCS Level II

The Difference Between ICD-10-CM, CPT, and HCPCS Level II

Introduction

Medical coding relies on several different code sets, and understanding the purpose of each one is an important part of learning how coding works. Three of the most commonly used are ICD-10-CM, CPT®, and HCPCS Level II.

Although these code sets often appear together on the same claim, they serve different purposes. ICD-10-CM primarily explains why the patient received care, while CPT® and HCPCS Level II generally describe the services, procedures, supplies, or other items provided.

Knowing which code set applies is about more than recognizing the format of a code. Coders also need to understand what each system represents, where it is commonly used, and how the code sets work together to tell the complete story of an encounter.

In this post, we'll take a quick look at each code set, when it is used, and some common mistakes to avoid—without getting buried in the thousands of codes and guidelines contained within them.

ICD-10-CM Overview

ICD-10-CM (International Classification of Diseases, Tenth Revision, Clinical Modification) is the code set used to report diagnoses, conditions, injuries, symptoms, and other reasons a patient receives healthcare services in the United States.

ICD-10-CM codes are organized into chapters based largely on body systems and types of conditions. Depending on the diagnosis, code selection may require details such as anatomical location, laterality, acuity, severity, associated conditions, or encounter type.

Coders use the Alphabetic Index to begin locating a diagnosis and the Tabular List to verify the final code selection and review applicable instructions. Coding conventions and the Official Guidelines for Coding and Reporting also help determine how codes should be assigned and sequenced.

In simple terms, ICD-10-CM helps communicate what condition is being evaluated, treated, or otherwise addressed during the encounter. It provides the diagnosis side of the coding picture and helps establish the medical necessity for the services reported.

CPT Overview

CPT® (Current Procedural Terminology) is the code set used to report many of the medical services and procedures performed by physicians and other qualified healthcare professionals. It is maintained and updated annually by the American Medical Association (AMA).

CPT® codes describe services such as office and hospital visits, surgical procedures, diagnostic testing, imaging, laboratory services, and many other professional healthcare services.

The code set is divided into major sections based on the type of service performed. Accurate code selection often depends on details within the documentation, including the procedure performed, anatomical location, technique, extent of the service, and other code-specific requirements.

CPT® also includes guidelines, parenthetical instructions, modifiers, and bundling considerations that can affect how a service is reported.

While ICD-10-CM generally communicates why the patient received care, CPT® helps communicate what service or procedure was performed.

HCPCS Level II Overview

HCPCS Level II (Healthcare Common Procedure Coding System) is used to report many healthcare products, supplies, medications, equipment, and services that are not represented by CPT® codes. The code set is maintained by the Centers for Medicare & Medicaid Services (CMS).

HCPCS Level II codes are alphanumeric and begin with a letter followed by four numbers. They may be used to report items and services such as:

• Ambulance services

• Durable medical equipment (DME)

• Prosthetics and orthotics

• Medical supplies

• Certain drugs and medications

• Some services not otherwise represented in CPT®

HCPCS Level II also includes modifiers that may provide additional information about how an item or service was provided.

While CPT® primarily describes medical procedures and professional services, HCPCS Level II helps capture many of the products, supplies, medications, and additional services involved in patient care.

When Each Is Used

These three code sets often work together to describe different parts of the same healthcare encounter. Which codes are needed depends on the services provided, the setting, and the payer's reporting requirements.

ICD-10-CM is used to report the patient's diagnoses, conditions, symptoms, injuries, and other reasons for the encounter. Diagnosis codes help explain the medical necessity for the services being provided.

CPT® is used to report many of the procedures and professional services performed during the encounter. This may include an E/M service, surgery, diagnostic test, imaging study, or other procedure.

HCPCS Level II is used when additional services or items need to be reported that aren't represented by CPT®. This commonly includes medications, supplies, durable medical equipment, and certain transportation or other services.

For example, a patient may receive an injection during an office visit. ICD-10-CM identifies the condition being treated, CPT® may identify the administration service, and HCPCS Level II may identify the medication that was administered.

Not every encounter requires codes from all three systems. The coder's job is to determine which code sets apply based on the documentation, services provided, and applicable coding and payer guidelines.

Common Mistakes

Because ICD-10-CM, CPT®, and HCPCS Level II may all be used during the same encounter, it is important to understand the role each code set plays. Some common mistakes include:

• Confusing diagnosis and procedure coding. ICD-10-CM describes diagnoses and conditions, while CPT® and HCPCS Level II generally report services, procedures, supplies, and other items provided.

• Assuming CPT® covers everything performed or supplied. Some medications, equipment, supplies, and services require HCPCS Level II codes instead.

• Selecting codes without enough documentation. Recognizing the service or diagnosis isn't enough—the documentation must support the specificity of the code selected.

• Ignoring code-set instructions. Each system has its own guidelines, conventions, instructional notes, and reporting requirements that must be followed.

• Overlooking payer requirements. A service may be coded differently depending on the payer or setting, particularly when HCPCS Level II codes are involved.

• Using outdated codes. All three code sets are updated regularly, so coders need to make sure they are working with the correct code set for the applicable date of service.

The code sets work together, but they are not interchangeable. Understanding what information you are trying to report is often the first step in knowing where to look for the appropriate code.

Conclusion

ICD-10-CM, CPT®, and HCPCS Level II each serve a different purpose, but together they help communicate the complete picture of the care a patient receives.

ICD-10-CM identifies the diagnoses and conditions, CPT® reports many of the services and procedures performed, and HCPCS Level II captures many of the supplies, medications, equipment, and additional services provided.

As you gain coding experience, recognizing which code set to use becomes much more natural. The important thing is to understand what you are trying to report, review the documentation carefully, and then apply the guidelines and instructions for the appropriate code set.

Learning how these systems work together provides a strong foundation for understanding the larger medical coding process—without needing to memorize every code along the way.

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