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Basic Medical Coding Systems

There are several coding systems that medical coders use in order to do their jobs. Each is designed with the same purpose: to help medical professionals communicate information about patients’ conditions, treatment and medical history. Three of the major coding systems in the US are the International Statistical Classification of Diseases and Related Health Problems (ICD), the Current Procedural Terminology (CPT) and the Healthcare Common Procedural Coding System (HCPCS). They are complex combinations of numbers and letters and cover tens of thousands of diseases, symptoms and conditions. Here’s a brief overview:

International Statistical Classification of Diseases and Related Health Problems (ICD): Published by the World Health Organization (WHO), this system follows that organization’s classification of diseases that is used around the world. The ICD is an alphanumeric system that is now in its 10th revision (ICD-10), with the 11th slated to take effect in 2015. Currently, there are over 155,000 codes in effect.

ICD-10 Code Categories:

  • A00-B99 Certain infectious and parasitic diseases
  • C00-D48 Neoplasms
  • D50-D89 Diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism
  • E00-E90 Endocrine, nutritional and metabolic diseases
  • F00-F99 Mental and behavioural disorders
  • G00-G99 Diseases of the nervous system
  • H00-H59 Diseases of the eye and adnexa
  • H60-H95 Diseases of the ear and mastoid process
  • I00-I99 Diseases of the circulatory system
  • J00-J99 Diseases of the respiratory system
  • K00-K93 Diseases of the digestive system
  • L00-L99 Diseases of the skin and subcutaneous tissue
  • M00-M99 Diseases of the musculoskeletal system and connective tissue
  • N00-N99 Diseases of the genitourinary system
  • O00-O99 Pregnancy, childbirth and the puerperium
  • P00-P96 Certain conditions originating in the perinatal period
  • Q00-Q99 Congenital malformations, deformations and chromosomal abnormalities
  • R00-R99 Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified
  • S00-T98 Injury, poisoning and certain other consequences of external causes
  • U00-U99 Codes for special purposes
  • V01-Y98 External causes of morbidity and mortality
  • Z00-Z99 Factors influencing health status and contact with health services

Current Procedural Terminology (CPT): CPT is a numeric code maintained by the American Medical Association (AMA) that contains over 8,500 codes. The AMA does not publish the codes free of charge, but there are three general categories of CPT codes:

  • Category I CPT Codes
  • Category II CPT Codes: Performance Measurement
  • Category III CPT Codes: Emerging Technology

Healthcare Common Procedural Coding System (HCPCS): This system is required by the Centers for Medicare and Medicaid Services (CMS). It is based on the CPT, with an added code used to bill Medicare, Medicaid and other health insurance programs in order to ensure that claims are processed in an orderly and consistent manner.

  • Level I consists of the CPT codes.
  • Level II codes are alphanumeric and primarily used to identify products and services not included in the CPT codes, like ambulance services and medical equipment, prosthetics, orthotics and supplies used outside a doctor’s office.