Medical Coding: Step By Step

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Medical documentation is essential to a medical coder's job. One major responsibility of a medical coder is to transform the information in medical records into diagnosis and procedure codes for billing. When coding physician notes, it is important to never assume. If you are unsure or unclear, always get clarification from the physician.   

There are two types of physician documentation that assist a medical coder in coding are office notes and operative notes.

  • Office notes consist of the patient's reason for visit, symptoms, illnesses and diagnoses, physician's findings, treatment plan, and follow-up plan.
  • Operative notes consist of the preoperative diagnosis, postoperative diagnosis, services and procedures performed, and a description of everything that occurred before, during, and after the procedure.

When clarifying documentation, ensure that all notes written by the physician support the diagnosis and procedures. Also, ensure that the diagnosis provides medical necessity for the procedures listed in the notes.

Assign ICD-10 Codes and CPT Codes

The medical coder must assign codes to diagnosis and procedures documented in the patient records.

Diagnosis Codes

Diagnosis codes are assigned from the International Classification of Diseases (ICD) book. The current edition is ICD-10.  ICD-10 was implemented by the Centers for Medicare and Medicaid Services (CMS) on October 1, 2015, replacing ICD-9. Services provided prior to October 1, 2015, must be billed with ICD-9 codes even if the services are not billed until after October 1, 2015. Services provided after the ICD-10 implementation on October 1, 2015, must be billed with ICD-10 codes.

Procedure Codes

Procedure codes are assigned from the Current Procedural Terminology (CPT) book as determined by the American Medical Association (AMA). The CPT book lists the CPT codes, the matching procedure  and definitions used by physicians, outpatient Hospitals, and ambulatory surgical centers (ASC). Hospital inpatient procedures are not listed in the CPT book. These codes are found in the ICD-10-PCS book, a replacement for ICD-9 Volume 3.

Stay Current on Coding Guidelines

  1. Visit the AMA website.  The site provides additions, expirations, updates, and revisions to the coding manual. The AMA website assists coders in keeping their professional knowledge and skills up-to-date, participate in events that help to develop and maintain coding competence, become familiar with guidelines and regulations, and obtain information to improve the quality of their work. AHIMA and AAPC also have websites that provide timely, detailed and up-to-date information to medical coders on a regular basis.
  2. Get CMS coding updates. CMS publishes updates to the CMS website annually. It also offers provider resources, statute and regulations, and provider-specific Medicare information. Medicare carriers are also an excellent source for regular update changes. Coders can sign up for listservs.
  3. Network with other coders. Coding is such a vast area, one coder cannot possibly know everything there is to know about coding. Sometimes coders run into situations in which they need additional assistance. Coders can be a great resource, often the best resource, for one another. While shared information is essential, it is important to be careful about what advice or assistance is accepted. Coding forums are one area to stay away from. Anyone can answer questions on coding forums which could lead a coder to violate coding regulations.
  4. Read the CPT instructions. Instructions in the CPT code manual are specifically there to assist coders with all pertinent information about coding such as how to find codes, categories of codes, descriptions of codes, what codes can be billed together and what codes should be billed alone.
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