Ann Dermatol.  2020 Apr;32(2):115-121. 10.5021/ad.2020.32.2.115.

Validity of Diagnostic Codes for Identification of Psoriasis Patients in Korea

  • 1Department of Dermatology, Ilsan Paik Hospital, Inje University College of Medicine, Goyang, Korea.
  • 2Department of Dermatology, Busan Paik Hospital, Inje University College of Medicine, Busan, Korea.
  • 3Department of Dermatology, Sanggye Paik Hospital, Inje University College of Medicine, Seoul, Korea.
  • 4Department of Dermatology, Haeundae Paik Hospital, Inje University College of Medicine, Busan, Korea.
  • 5Department of Dermatology, Seoul Paik Hospital, Inje University College of Medicine, Seoul, Korea.


Recently, the number of nationwide medical researches on psoriasis using the National Health Insurance Service database has been on the rise. However, identification of psoriasis using diagnostic codes alone can lead to misclassification. Accuracy of the diagnostic codes and their concordance with medical records should be validated first to identify psoriasis patients correctly.
To validate the diagnostic codes of psoriasis (International Classification of Diseases, 10th Revision L40) and to find the algorithm for the identification of psoriasis.
We collected medical records of patients who received their first diagnostic codes of psoriasis during 5 years from five hospitals. Fifteen percent of psoriasis patients were randomly selected from each hospital. We performed a validation by reviewing medical records and compared 5 algorithms to identify the best algorithm.
Total of 538 cases were reviewed and classified as psoriasis (n=368), not psoriasis (n=159), and questionable (n=11). The most accurate algorithm was including patients with ≥1 visits with psoriasis as primary diagnostic codes and prescription of vitamin D derivatives. Its positive predictive value was 96.5% (95% confidence interval [CI], 93.9%~98.1%), which was significantly higher than those of the algorithm, including patients with ≥1 visits with psoriasis as primary diagnostic codes or including ≥1 visits with diagnostic codes of psoriasis (primary or additional) (91.0% and 69.8%). Sensitivity was 90.8% (95% CI, 87.2%~93.4%) and specificity was 92.5% (95% CI, 86.9%~95.9%).
Our study demonstrates a validated algorithm to identify psoriasis, which will be useful for the nationwide population-based study of psoriasis in Korea.


Electronic medical record; International Classification of Disease Codes; National Health Insurance; Psoriasis

MeSH Terms

Electronic Health Records
International Classification of Diseases
Medical Records
National Health Programs
Sensitivity and Specificity
Vitamin D
Vitamin D


  • Fig. 1 Flow chart of study population selection. Total 3,587 patients with psoriasis diagnostic codes were included. Random samples of 538 cases were collected (15% of total cases from each hospital). After the review, 368 (68.4%) were psoriasis, 159 (29.6%) were not psoriasis, and 11 (2.0%) were questionable to diagnosis. ICD: International Classification of Diseases.


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