Medical Codings – An Overview

Bertillon Classification of Causes of Death, introduced by a French physician in 1893 at a congress of International Statistical Institute in Chicago, is generally considered the origin of the most well known medical coding ICD - 'International Classification of Diseases', currently being used to classify the causes of mortality as well as morbidity (diseases and other health related problems).

The primary purpose of a medical coding is to apply codes to clinical terms or information. In its simplest form you can think of it as a dictionary mapping clinical terms to codes (where each term is associated with a unique code). It is an integral part of clinical documentation. Classically it's being used to generate statistical reports. Coding the diagnostic and treatment information in insurance claims is another common use of it.

Medical classification is being used internationally for more than hundred years, but it is the advancement in information technology that opened up new avenues, gave new dimensions and created new opportunities for medical coding. It is no more being used only for statistical and billing purposes but a wide range of uses have been emerged since the start of electronic health records. These uses include interoperable health records, exchange of health records between systems, intelligent decision support system, to name but a few. In the last few decades several standards of classification have been developed covering not only diagnostic but also other clinical information like  services and procedures delivered to the patients.

In this article I will be giving an overview of a few of most common medical coding standards hoping healthcare managers specially healthcare IT staff will benefit from it.

ICD

As mentioned earlier International Classification of Diseases is a global standard to classify diseases. It is a coding system to classify diseases, diagnosis, symptoms and other health related problems. It is maintained by World Health Organization (WHO). WHO periodically revises the code set and ICD-10 is its widely used version currently.

ICD is being used in many countries to generate statistical reports on mortality and morbidity. Besides, one of its most common usages is for billing purpose. Combined with services or procedures codes it forms the basis of payment claims. In those claims healthcare providers use ICD code to specify why a particular procedure was delivered to the patient.

ICD-10 code list is divided in chapters, most of the chapters are associated with a particular body system. For instance, chapter XI is for the diseases of digestive system. All of the codes in that chapter start with letter 'K'. For example, K70 is the code for 'Alcoholic liver disease' and K70.4 is the code for 'Alcoholic cirrhosis of liver'.

An important point to note here it that certain countries have developed their own customized ICD code sets. For example ICD-10-CM is the modified version of ICD-10, implemented in United States. National Center for Health Statistics (NCHS) and Center for Medicare and Medicaid Service (CMS) in USA are responsible for ICD-10-CM (Clinical Modification). ICD-10-CM has more than 68,000 codes as compare to around 14,400 codes in ICD-10 (WHO version).

SNOMED CT

Systematized Nomenclature of Medicine Clinical Terms is by far the most comprehensive multi-lingual clinical terminology ever developed. It is maintained and distributed by a non-profit standards development organization IHTSDO (International Health Terminology Standards Development Organization) and covers clinical findings, diseases, procedures, body structure, treatments, drugs, devices etc. It has more than 311,000 codes each representing a unique clinical concept or term.

SNOMED CT is a structured collection of medical terms very suitable for clinicians to capture health related information of their patients through electronic health records system. It enables healthcare provider to code patient's health related information in a very clear and accurate way without loosing valuable details (that is not possible with classification system like ICD).

By allowing healthcare providers to capture and code detailed and accurate information in EHR it yields a lot of benefits:

• It makes electronic health record interoperable with other systems. It provides a consistent medical terminology that enables healthcare records to be exchanged or understood anywhere in the world without loosing any valuable detail.
• It enables efficient search of patients records for relevant and useful information
• It can also be used in clinical decision support system and in automatic identification of patient risk factors.
• It makes it possible to do an effective analysis of data at different levels of aggregation, also very useful for medical research.
• It allows monitoring of disease trends at population level

It is its vital role in EHR and its importance in medical coding that warrants to go little deeper here and see what makes it a unique coding system in medical ontology.

• Concept
• Descriptions
• Relationships

Concept and description: Concept basically is a clinical term identified by a unique code known as concept ID. The concept is always associated with at least two descriptions 'fully specified name' and 'preferred term'. It can also be associated with multiple synonyms. For example, 22298006 is a concept ID in SNOMED CT, its fully specified name is 'Myocardial infarction (disorder)' its preferred term is 'Myocardial infarction'. Heart attack, Infarction of heart, and Myocardial infarct are acceptable synonyms for this concept.

Relationships: The power of this ontology rests in relationships. It is relationships that stands SNOMED CT out among other coding systems. Relationship links a concept to other concepts that have related meaning. Though a concept always has one relationship many of the codes have multiple relationships. Relationship defines what kind of concept it is. It also enables data to be analyzed at various aggregation levels.

Below is a simplified example of how a concept 'Pneumonia' (a disease) is linked with other concepts in SNOMED CT:

CPT

Current Procedural Terminology - also known as HCPCS (Health Care Common Procedure Coding System) Level 1 -  is developed and maintained by American Medical Association. It is used to identify and report medical procedures and services delivered to the patients. It contains more than 8,000 codes mostly used for outpatient services and procedures. It is widely used to in claims processing. It tells what services were delivered to the patients while ICD codes tell why those services were delivered.

Besides, above three coding standards there are a lot of other coding systems targeting specific domains or needs. For example, HCPCS Level 2 covers supplies, equipment, devices, procedures, and other non-physician services not covered by CPT. LOINC (Logical Observation Identifiers Names and Codes) is a specialized ontology to capture and exchange laboratory and clinical results. CDT (Current Dental Terminology), developed and maintained by American Dental Association, is used to document and report dental treatment and procedures.

Nevertheless, medical coding is sometimes confusing for those who are not formally trained or experienced in EHR domain. This article is an humble attempt to explain the concept and purpose of medical coding hoping it would encourage healthcare managers to do further research in this area before implementing the coding system(s) in their organization and guide their team in the right direction.