Reimbursement claims actually require 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 you do, and ICD-9 codes describe why you do it.