The Basics of Clinical Coding: CPT and ICD-10-CM

The medical billing and coding professional will need to become very familiar with clinical coding using the basic ICD-10-CM & CPT coding system as this will be used for clinical coding on patient charting and medical insurance billing. Clinical coding will identify procedures and conditions that the physician will need to report on based on patient diagnosis. The ICD-10-CM is broken into the Alphabetic Index and Tabular Index that work together to create clinical coding used by the medical billing and coding assistant. As a medical biller and coding professional, you will need to know how to locate a code in the ICD-10-CM & CPT. They will also need to understand the basic definition of a medical diagnosis and medical procedure.

What is Clinical Coding?

Coding is the transformation of verbal descriptions into numbers. Assigning numeric or alphanumeric codes for clinical procedures and conditions. A clinical code can be part of a classification system that groups similar diseases and procedures together, helping to organize related medical information. The classification system used in the United States is the International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM). The official version of the ICD-10-CM guidelines are approved by the Cooperating Parties for the ICD-10-CM including members from the American Hospital Association (AMA), the American Health Information Management Association (AHMA), Centers for Medicare and Medicaid Services (CMS) and National Center for Health Statistics (NCHS). The CPT & HCPCS coding systems are maintained by with the Centers for Medicare & Medicaid Services.

The clinical coding conventions for ICD-10-CM address the structure and format of the coding system, including an Alphabetic Index, Tabular List and the rules and instructions that a medical billing and coding assistant must follow. Clinical codes consist of three to seven basic characters. The first three characters identify the category of the clinical code, the next three characters identify the etiology, anatomic site and the severity, and the seventh character can be used to add a specificity to the clinical code.

Abbreviations are used in ICD-10-CM including “not elsewhere classifiable”(NEC) and “not otherwise specified”(NOS). Punctuation is used in the coding system including brackets, parentheses and colons. Square brackets are a punctuation mark used in the Tabular List to enclose synonyms, abbreviations, alternative wording or explanatory phrases. Slanted brackets are used in the Alphabetic Index to identify manifestation codes. The manifestation code represents a secondary condition that was caused by the primary condition. Parentheses are a punctuation mark that encloses supplementary words or explanatory information not present in the statement of the diagnosis. The colon is a punctuation term that is used in the Tabular List after an incomplete term that needs additional terms to assign a specific clinical code.

The Alphabetic Index

The Alphabetic Index is divided into two parts 1) the index to diseases and injury 2) index to external causes of injury. It is designed to allow medical billing and coding assistants to look up medical terms and connect them with the appropriate ICD codes.

The Tabular List

The Tabular List is a numerical listing of all codes. It is divided into 21 chapters and focus on the body or organ system and certain infectious and parasitic diseases. The first character of an ICD-10-CM code is always an alphabetic letter. All letters of the alphabet are used except for the letter U that is reserved by the World Health Organization (WHO) for new diseases and for bacterial agents resistant to antibiotics.

Locating a Code in the ICD-10-CM

The medical billing and coding professional must use both the Alphabetic Index and Tabular List to assign a clinical code. The medical billing and coder will identify the main term and any sub-terms in the Alphabetic Index. The clinical code in the Alphabetic Index is then verified by the Tabular List. Diagnosis codes are to be reported with the highest number of characters available.

What is a Medical Diagnosis?

A diagnosis is a word or phrase used by a medical professional to identify a disease or condition a patient suffers from, for which the patient needs medical care. A diagnosis is identified after a physical exam of the patient. Clinical CPT codes that describe signs and symptoms may be used if that is the only thing the physician knows about the patient’s condition. If the patient is suffering from an acute or chronic condition, the medical billing and coding professional must identify, in the Alphabetic Index, if there are separate entries at the same indentation level.

What is a Medical Procedure?

A medical procedure is a medical surgery or therapeutic procedure on or within the patient’s body that is intended to achieve a result for the patient.


Familiarity with using the ICD-10-CM & CPT coding system is an important part of a medical billing and coding professional’s job.  The ICD-10-CM coding system can be learned by attending a vocational school which offers courses on this topic.

Are you interested in learning more about basic clinical coding, CPT codes and ICD-10-CM coding systems? Gwinnett Colleges & Institute’s Medical Billing and Coding programs will provide you with the opportunity to learn insurance coding and processing, medical administrative procedures, and the regulatory requirements in the healthcare delivery system.  School externships provide the opportunity to apply the medical billing and coding skills learned in the classroom in actual medical settings. Gwinnett Colleges & Institute offers medical billing & coding courses to gain essential skills and training to achieve entry-level positions in this career field. These medical billing & coding courses will be the first step in starting a rewarding career.

Contact us to learn more about how you can become a medical billing and coding assistant today.