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Limits of ICD-9-CM code usefulness in epidemiological studies of contact and other types of dermatitis
1Division of Dermatology and Cutaneous Surgery, Department of Internal Medicine, College of Medicine, University of South Florida, Tampa, FL 33612, USA.
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.
