Limits of ICD-9-CM code usefulness in epidemiological studies of contact and other types of dermatitis.

BACKGROUND: International Classification of Diseases, Version 9, Clinical Modification (ICD-9-CM) coding information used for billing is readily available in computerized form.

OBJECTIVES: The purpose of this article is to determine the usefulness of ICD-9-CM codes in a descriptive dermatoepidemiological study of contact and other dermatitis.

METHODS: Prospective recording of specific dermatologic diagnoses and the ICD-9-CM code assigned for each diagnosis was performed for all patient visits to the author's dermatology clinics for 6 months.

RESULTS: There were 2,524 patient visits with 4,451 diagnoses, of which 789 diagnoses were dermatitis. The 10 different diagnostic categories of dermatitis had eight associated ICD-9-CM codes. Allergic contact dermatitis with 247 visits, irritant contact dermatitis with 30 visits, and nummular dermatitis with 61 visits shared one diagnostic code. Thus, 43% of visits for dermatitis were intermixed by having the same ICD-9-CM code.

CONCLUSION: Lack of one-to-one correspondence of ICD-9-CM codes with dermatitis diagnostic categories creates a situation in which ICD-9-CM codes are not useful for dermatoepidemiological studies of contact and other types of dermatitis. This could be corrected by assigning additional five-digit ICD-9-CM codes to cover each type of dermatitis. Coding for specific allergens or irritants is not feasible with the current five-digit ICD-9-CM codes.