Imprecise Coding in Allergic Contact Dermatitis: A Register-Study From Northern Finland Between Years 1999 and 2022

Background

Registry-based data are increasingly used in dermatological research. A recent epidemiological study has shown that the use of non-specific diagnostic codes is common among dermatologists.

Objectives

To study closely the use of the diagnostic codes L23.8 (‘allergic contact dermatitis [ACD] for other agents’) and L23.9 (‘ACD with unspecified cause’) by using single-centre data.

Patients/Materials/Methods

This retrospective study included all patients whose record contained at least one entry of either code, recorded at the Oulu University Hospital, Finland, between the Years 1999 and 2022.

Results

The database search retrieved records of 472 patients with the L23.8 code, 264 patients with L23.9. Over the 20-year follow-up period, the use of L23.8 increased and that of L23.9 decreased. In most (85.1%) cases, the L23.8 code was used even though the more specified L23 code could have been chosen. In one-third of cases, L23.8 was used to cover ACD with multiple allergens that would otherwise be identified by their specific sub-codes. The L23.9 code was used most often prior to patch testing (69.1% cases).

Conclusions

This study revealed several imprecisions in the use of both codes. Our study highlights the importance of correct coding in clinical practice, as it emphasises the most common pitfalls.