ICD-10 includes 68,000 diagnosis codes, compared to 13,000 in ICD-9, while inpatient procedure codes in ICD-10 grow to 87,000 from only 11,000 in ICD-9. The new codes in ICD-10 provide greater clinical detail and cover medical treatments and technologies not reflected in the older ICD-9 codes.
CMS has said that while ICD-10 expands the number of codes, a large portion of ICD-10 codes only differ in one parameter. For example, nearly 25% of ICD-10 codes are the same except for indicating the right side of the patient's body versus the left. Another 25% of the codes differ only in the way they distinguish among "initial encounter," versus "subsequent encounter," versus "sequelae." Sequelae refers to conditions that are usually the aftermath of another disease, injury, or event, such as neck pain resulting from whiplash suffered in an auto accident.
Yet the increased code detail in ICD-10 means that required clinical documentation by providers "will change substantially." CMS says ICD-10 includes a more robust definition of severity, comorbidities, complications, sequelae, manifestations, causes, and a variety of other important parameters that characterize the patient's condition.
Even the American Medical Association, whose members have opposed ICD-10 because of the burdens and expense the conversion puts on doctor practices, acknowledges that the additional codes allowed by ICD-10 offer more flexibility than what's offered by ICD-9.