Report
Potential misclassification of patients with psoriasis in electronic databases

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Background

Electronic claims and medical record databases are increasingly used for observational studies of psoriasis. The purpose of this study was to assess the validity of psoriasis diagnostic codes in an electronic database.

Methods

This study was performed in a population-based setting in Olmsted County, Minnesota, where all diagnoses and procedures from all health care providers in a large community are indexed and recorded in an electronic database. The database was searched for patients aged 18 years or older with diagnostic codes consistent with psoriasis for the time period January 1, 1976, to January 1, 2000. The complete medical records of all patients were reviewed manually for validation of psoriasis diagnoses.

Results

We reviewed the complete medical records of 2556 patients with at least one diagnostic code consistent with psoriasis. Based on medical record review, 1458 (57.0%) patients were confirmed to have psoriasis, of which the majority (81%) received confirmation by a dermatologist. The most commonly used diagnostic codes for psoriasis were International Classification of Diseases, Ninth Revision 696.1 (psoriasis, not otherwise specified) with a positive predictive value of 68.7% (95% confidence interval: 66.5%, 70.9%). Increasing frequency of codes in a given time window was associated with positive predictive values. However, positive predictive value for only one code in a 5-year time window was still as high as 60% (95% confidence interval: 57%, 63%).

Limitations

Differences between individual electronic medical record databases may limit the ability to form a general conclusion from these findings. The remitting, relapsing course of psoriasis and the heterogeneity in clinical presentation create challenges in case ascertainment.

Conclusion

Electronic identification of patients with psoriasis by diagnostic codes alone may lead to misclassification in database studies.

Section snippets

Methods

This was a retrospective study using the data resources of the Rochester Epidemiology Project (REP). As described previously, REP is a centralized medical records linkage system that encompasses all health care delivered to residents of Olmsted County, Minnesota.12 All health care providers in this county use a unit medical record system whereby all medical information on each individual is accumulated within a single dossier. Furthermore, detailed indices containing all clinical, surgical, and

Results

We identified a total of 2556 potential patients with diagnostic codes consistent with psoriasis between 1976 and 2000. After manual screening of the medical records from all health care providers, 1458 (57.0%) patients with psoriasis were confirmed as having incident psoriasis. Of the remaining 1098 patients, 62.4% had diagnoses other than psoriasis (eg, parapsoriasis, pityriasis rosea, psoriasiform dermatitis) and 37.6% had prevalent conditions (ie, psoriasis before study time frame or moved

Discussion

In this study, we report on the validity of psoriasis diagnostic codes in an electronic medical record database. Both the type and frequency of psoriasis codes influence the validity of identification of patients with psoriasis. The PPV remains as high as 60% for a single psoriasis code in a 5-year time window, indicating that the relapsing and remitting disease course in psoriasis may challenge electronic identification of patients with psoriasis in database studies. These findings indicate

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Supported by an unrestricted research grant from Amgen Inc.

Disclosure: Dr Maradit Kremers has received consulting fees, speaking fees, and/or honoraria (less than $10,000) from Amgen. Drs Icen, Crowson, McEvoy, and Gabriel have no conflicts of interest to declare.

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