“So, What Do You Do?” A Simple Explanation of Medical Coding

What does a medical coder do? Put simply, a medical coder reviews clinical documentation and translates a patient’s diagnoses, visits, services and procedures into standardized medical codes. These codes support accurate billing, reimbursement, compliance, reporting and healthcare data.

Of course, that explanation may still earn you a blank stare—especially from someone who assumes “coding” means fixing computers.

A simpler way to explain medical coding is to break it into four basic pieces:

• E/M codes identify the visit.

• ICD-10-CM codes explain why the patient needed care.

• ICD-10-PCS and CPT codes identify what happened.

• Modifiers provide additional details.

This framework does not cover every code set, care setting or coding rule, but it provides an easy starting point for understanding what medical coders do and how they turn a patient encounter into a coded story.

Tell someone you are a medical coder, and there is a good chance they will assume you write computer code. Once you clarify that you work in healthcare, the next question is often:

  So…what exactly do you do?”

This is where the explanation can get complicated.

You could start talking about code sets, official guidelines, medical necessity, documentation requirements, payer rules, and compliance. But unless the person asking is also a coder, you may lose them somewhere around the second acronym.

Fortunately, there is a much simpler way to explain the basic pieces of medical coding:

• Evaluation and Management (E/M) codes identify the type of visit
• ICD-10-CM codes tell us the why
• ICD-10-PCS and CPT codes tell us what happened
• Modifiers give us additional details

This explanation does not cover every code set, care setting or coding rule—but it gives someone outside the profession a good place to start.

E/M = The Visit

What type of visit took place, and what level of evaluation and management service did the provider perform?

E/M codes represent visits and related services, including office visits, hospital care, emergency department services and consultations when applicable.

Selection of a code depends on factors such as medical decision making or time spent with the patient and the specific rules for a particular category of service. Coders must understand both the documentation and the E/M guidelines to determine what can be reported.

Technically, E/M codes are part of CPT. But when you are explaining coding to someone new, it can be useful to give “the visit” its own place in the conversation because it is such a large and important area of coding.

ICD-10-CM = Why

Why is the patient being seen?

ICD-10-CM codes describe the patient’s diagnosis, condition, symptom, or reason for the encounter. They help explain the medical need behind the care provided.

Depending on the encounter, the “why” could be:

• A confirmed condition, such as pneumonia
• A symptom, such as chest pain
• An injury, such as a sprained ankle
• A reason for care, such as a screening examination

Of course, selecting the correct diagnosis code involves much more than memorizing codes or finding a term in an index. Coders must review the documentation, apply the relevant guidelines, and determine which details are supported. But when explaining ICD-10-CM to someone unfamiliar with coding, “the why” is a helpful shortcut.

CPT = What

What service or procedure was provided?

CPT codes identify many of the medical services and procedures provided to patients. These may include surgeries, diagnostic testing, imaging, laboratory services, and other treatments.

If ICD-10-CM explains why the patient needed care, CPT identifies the care provided.

For example, if the diagnosis code tells us that a patient has knee pain, the CPT code tells us what service or procedure was provided to evaluate or treat the pain, such as an X-ray, an injection, or a surgical procedure.

The “what” sounds straightforward—until you realize a coder must determine the exact procedure performed, the approach used, the anatomical site involved, and whether the documentation supports every element of the selected code. One small word in an operative report can change which code is selected.

It's easy to see that medical coders do far more than simply match terms to numbers.

Modifiers = The Details

On some occasions, additional circumstances not identified by the CPT code affect how the service or procedure was provided.

Modifiers are additional two-character codes appended to CPT codes when further explanation about those circumstances is needed, but without changing the basic service being reported.

Depending on the situation, a modifier may indicate that:

• A procedure was performed on a particular side of the body
• Multiple procedures were performed
• A service was reduced or discontinued
• A separate and distinct service was provided
• An assistant participated in the surgery

Modifiers may seem small, but they can have a significant effect on how a claim is understood, processed, and paid. They are the details—and in coding, the details matter.

Putting It All Together

Imagine that a patient goes to the emergency department after twisting an ankle.

• The visit: The patient is evaluated in the emergency department. The appropriate E/M code for an emergency department encounter represents the visit.
• Why: The patient has an ankle injury and pain. The ICD-10-CM code communicates the diagnosis or reason for the encounter.
• What: An X-ray is performed. The CPT code communicates the service provided.
• The details: The patient's left ankle was injured. The appropriate modifier supplies the detail of laterality.

The encounter becomes a coded story: what kind of visit occurred, why the patient needed care, what was done, and which details affected the services.

The Simple Explanation—and the Real Job

The visit, the why, the what, and the details make medical coding easier to explain. The coder’s actual work, however, is anything but simple.

Medical coders interpret clinical documentation, understand anatomy and medical terminology, apply official guidelines, follow setting-specific rules and identify when the record does—or does not—support a code. They help turn the patient encounter into standardized information used for reimbursement, reporting, compliance, and healthcare data.

So, the next time someone asks what you do, you can skip the long list of acronyms and start here:

• E/M tells us about the visit.
• ICD-10-CM tells us why.
• CPT tells us what.
• Modifiers give us the details.

And if they still think you build websites, you can always tell them your kind of coding comes with considerably more anatomy.

Frequently Asked Questions

HIAlearn, powered by Health Information Associates (HIA)—a leader in medical coding and auditing for more than three decades—offers a flexible, online education platform designed for today’s coders. With a growing catalog of AHIMA and AAPC-approved coding courses, HIAlearn supports both beginners and experienced coders looking to build confidence, accuracy, and CEU credits.

Courses are available across various coding types including CPT, E/M, ICD-10-CM, and ICD-10-PCS, and are designed for multiple specialties including inpatient, outpatient, profee, and CDI.

To stay up to date, coders can explore our Coding Updates hub for the latest ICD-10-CM, ICD-10-PCS, CPT, and IPPS changes. HIAlearn also supports organizations with group discounts and scalable team access, promoting accuracy, compliance, and continuous professional development across departments.

The information contained in this blog post is valid at the time of posting. Viewers are encouraged to research subsequent official guidance in the areas associated with the topic as they can change rapidly.