CPT vs. ICD-10 Codes: Mapping the ‘Why’ and ‘What’ of Rehab Therapy Patient Journeys

According to numbers from the American Physical Therapy Association (APTA), upwards of 300 million patient sessions occur each year throughout the U.S. For each of them, accurate documentation and billing are critical for both the patient’s care and the financial health of the healthcare facility. At the heart of this process is the use of two distinctive yet symbiotic code-based languages: ICD-10 and CPT® codes.

While each type of code serves important roles in patient care and reimbursement, they do so in different ways. Together, however, IDC-10 and the CPT® codes paint a full picture of the patient’s journey toward recovery while ensuring this journey is properly tracked and reimbursed.

In this post, we break down the key differences between ICD-10 and CPT® codes in rehab therapy, explaining when to use each and how they impact documentation and reimbursement.

What Are ICD-10 Codes?

ICD-10 codes, or the International Classification of Diseases, 10th Revision, are a global standard for documenting medical diagnoses. Developed by the World Health Organization (WHO), these codes provide a systematic way to classify diseases, injuries, and health conditions that impact patients.

In the U.S., the healthcare system uses a variant of ICD-10 called the ICD-10 Clinical Modification (ICD-10-CM), which was developed and is overseen by the Centers for Medicare and Medicaid Services (CMS). Today, there are over 69,000 ICD-10-CM diagnosis codes available for use by U.S. healthcare providers, including rehab therapists.

ICD-10 codes define why a patient is receiving care, highlighting the underlying diagnosis or condition that necessitates treatment. These codes offer a precise description of the patient’s health issue, whether it’s a musculoskeletal disorder, neurological condition, or an injury.

Rehab therapists use ICD-10 codes to communicate the medical necessity for the therapy being provided. For example, if a patient is recovering from a stroke and requires physical or occupational therapy, the ICD-10 code for the stroke diagnosis (i.e. I63.9) will be used to document the condition.

Payers look for codes that match the treatment to a medically necessary diagnosis. Therefore, ICD-10 codes directly impact the approval of therapy sessions and continued coverage, making them a critical part of the billing process. Without the correct ICD-10 code, claims may be denied and payments delayed.

What Are CPT Codes?

CPT® codes, or Current Procedural Terminology codes, are a standardized system used to describe the specific services and procedures provided to a patient. Unlike ICD-10 codes, which identify the diagnosis or medical condition, CPT® codes focus on documenting the what—that is, the treatment or service delivered.

Managed by the American Medical Association (AMA), CPT® codes are essential in accurately capturing and billing for the services performed by healthcare providers, including those in rehab therapy. The primary role of CPT® codes in the healthcare system is to describe the procedures or services a healthcare provider delivers during treatment. In rehab therapy, these codes represent everything from initial patient evaluations to the specific exercises, manual therapies, and modalities applied in a session.

For example, if a physical therapist conducts therapeutic exercises (CPT code 97110) or uses electrical stimulation (CPT code 97032) during a session, they must use specific CPT® codes to document and bill for those services. Using the correct current procedural terminology codes is therefore crucial for providers to receive proper reimbursement when performing medical procedures.

Each CPT® code has a corresponding description, ensuring that the services provided are clearly communicated for documentation and billing purposes. This standardized language simplifies the process of conveying what treatments were performed and helps healthcare providers ensure that they’re accurately billing for the time and effort spent on a patient’s care.

Some common CPT® codes in rehab therapy include:

• CPT Code 97110 – Therapeutic exercises
• CPT Code 97140 – Manual therapy techniques
• CPT Code 97116 – Gait training
• CPT Code 97530 – Therapeutic activities
• CPT Code 97150 – Group therapy
• CPT Code 97115 – Neuromuscular re-education

Aside from directly impacting how a rehab therapist gets paid, the use of accurate CPT® codes also facilitates communication between healthcare providers and insurance companies about the types and intensities of services provided during rehab therapy. Because of this, inaccurate coding can lead to underpayments, claim rejections, and even audits.

Key Differences Between ICD-10 and CPT Codes

While the use of both ICD-10 and CPT® codes is integral to rehab therapy, each type of code serves distinctly different functions in documentation, billing, and reimbursement. Rehab practitioners must understand these differences to ensure accuracy in both clinical documentation and revenue cycle management.

Purpose: Diagnosis vs. Procedure

As stated earlier, the most significant difference between ICD-10 and CPT codes lies in what they represent.

• ICD-10 codes focus on the diagnosis—describing a patient’s medical condition, injury, or illness. These codes explain why the patient is receiving treatment. For instance, ICD-10 code M54.5 represents lower back pain (unspecified), indicating that the patient has a condition that can be effectively treated with physical therapy.
• CPT® codes, on the other hand, describe procedures and services provided by a rehab therapist during treatment. CPT® codes detail what was done, such as 97110 for therapeutic exercises or 97140 for manual therapy techniques. These codes document the specific services provided in response to the patient’s condition.

Documentation: Initial Evaluation vs. Each Treatment Session

The time at which each code-based language is used is also a point of differentiation between ICD-10 and CPT codes.

• ICD-10 codes are typically used in the initial evaluation of a patient, providing a clinical rationale for why rehab therapy is required. A valid diagnosis code is necessary to prove that a patient needs or can benefit from rehab therapy services. For example, if a patient is diagnosed with lateral epicondylitis (tennis elbow) in the right elbow, the therapist must use ICD-10 code M77.11 to document the condition.
• CPT® codes are used during each treatment session to describe the services rendered. These codes ensure that the therapy provided is recorded accurately in the patient’s medical record. Every session will include one or more CPT® codes to detail what was done during that appointment, whether it’s an initial evaluation, hands-on treatment, or follow-up procedures. CPT® codes may also document remote therapeutic monitoring (RTM) services that occur between rehab therapy visits.

Reimbursement: Medical Necessity vs. Service Payment

Each code plays a different role during the payer reimbursement process, as well. For example:

• ICD-10 codes help prove that the rehab therapy is addressing a legitimate health concern and is not elective or unnecessary. Without a valid diagnosis, insurers will likely not approve or reimburse for the care provided.
• CPT® codes directly impact how much a therapist is paid for their services. Each CPT® code corresponds to a specific service, and private and public payers use these codes to determine appropriate reimbursement rates. Therefore, the more accurately CPT® codes are documented, the more precise and seamless the billing process generally is.

Coding Complexity and Updates

ICD-10 codes are typically more detailed and specific when it comes to diagnosis, with thousands of codes representing a wide variety of medical conditions. This complexity makes choosing the correct diagnosis code challenging, especially when the patient’s condition doesn’t fit neatly into a predefined category.

The hyper-specificity of ICD-10-CM coding has also led many billers to lampoon some of the more bizarre circumstances for which codes were created. These include codes created for those who have “walked into [a] lamppost” (W220.2XD), were “struck by a duck” (W61.62XD), or who was a “spacecraft collision injury occupant” (V95.43XS).

CMS provides annual updates to its ICD-10-CM coding system. While not as complex or vast as ICD codes, CPT® codes are also updated annually (by the AMA), so therapists must be proactive in staying current with code changes that apply to their operations and services.

Adding to the complexity of CPT® codes, however, is the use of modifiers. In coding, modifiers are applied (whenever necessary) to provide more specific details about the service provided. For example, modifier 59 might be used in rehab therapy to indicate that two separate medical procedures were performed on the same day that are not typically done together. Another common example is modifier KX, which is used when a medically necessary service exceeds a certain limit (i.e. the Medicare therapy cap).

What is Code Linkage?

As both ICD-10 codes and CPT® codes are used to tell a cohesive story about the patient’s care, it’s critical the codes match. In other words, the treatments and procedures used on the patient must make sense based on the diagnosis. This is called code linkage or code matching.

As we’ve clearly established, the ICD-10 diagnosis codes explain the why behind the treatment, while the CPT® code is a procedure coding system that explains what the treatments are. For medical billing to go smoothly, these two codes need to align logically. If they don’t, insurance companies may deny the claim because it raises questions about whether the treatment provided was necessary for the diagnosis given.

For example, if the ICD-10 code indicates a diagnosis of a sprained ankle but the CPT® code lists a treatment for a shoulder injury, the mismatch would likely result in a claim rejection or denial. Ensuring proper code linkage generally leads to smoother reimbursement and fewer delays. This alignment also helps reduce the risk of audits or compliance issues, as payers can see that the care provided directly addresses the patient’s condition.

Improve Your Coding Knowledge Base and Tools

To keep coding accurate and up to date, it’s essential rehab therapists regularly invest in education and stay informed about updates to both ICD-10 and CPT® codes. Attending workshops, subscribing to coding newsletters, or working with coding specialists can make a considerable difference in staying compliant and avoiding costly errors.

It’s also important to review documentation habits and ensure that clinical notes are thorough enough to support the codes being used. In other words, also practice defensible documentation. Fortunately, many modern physical therapy EHR solutions offer automated coding assistance, which can take much of the guesswork out of accurate coding processes. These systems help flag discrepancies, suggest the correct codes based on the documentation, and even assist with modifiers, all of which lead to more accurate billing and optimal reimbursement.

Leveraging these tools may not only reduce administrative burdens but also ensure your practice remains on top of the latest coding standards with minimal hassle.