Clinicians who must select ICD-9-CM diagnosis codes should use codes that provide the highest degree of accuracy and completeness (i.e., the greatest specificity). That usually means providing an ICD-9-CM code carried to the fifth digit. The Centers for Medicare and Medicaid Services (CMS) require all Medicare practitioners to use ICD-9-CM diagnosis codes with the highest specificity per the Health Insurance Portability and Accountability Act (HIPAA), as do most private payers. For example, clinicians using code 784.6 (symbolic dysfunction) to describe language/cognitive impairments of an organic nature may have this code rejected. Because this code category has fifth-digit subclassifications, the clinician should select the most appropriate subclassification. This might be 784.60 (symbolic dysfunction, unspecified), 784.61 (alexia and dyslexia) or 784.69 (other; acalculia, agnosia, agraphia, apraxia). Code 784.69 is intended to include multiple diagnoses, some of which may differ significantly, but it provides the highest level of specificity in that category and therefore should be used instead of 784.6. Clinicians should keep in mind that 784.60, 784.61, and 784.69 are subclassifications of 784.6, so using one of the subclassifications does not exclude 784.6.
Following the specificity rule, therefore, clinicians should assign 3-digit codes when there are no 4-digit codes within the category. Assign 4-digit codes if there is no fifth-digit subclassification for a particular category. Assign the fifth-digit subclassification code for those categories where it exits.
Clinicians should also be aware that codes marked NOS (not otherwise specified) or "unspecified" indicate that there is insufficient information in the medical record to assign a more specific code. NEC (not elsewhere classifiable) means that ICD-9-CM does not have a code that describes the condition.