ICD-9 vs. CPT Coding In the world of medical billing, coding of the medical billing forms actually requires the use of two coding systems, one that identifies the patient’s disease or physical state (the International Classification of Diseases, 9th Revision, Clinical Modification, or ICD-9-CM, codes) and another that describes the procedures, services or supplies you provide to your patients (the Current Procedural Terminology, or CPT codes). To differentiate between these coding systems, think of it this way: CPT codes describe what services you perform, and ICD-9 codes describe why you do it. Each service you render to a patient becomes a line on an insurance claim form. Your level of …