Validity of First-Time Diagnoses of Inherited Ichthyosis in the Danish National Patient Registry and the Danish Pathology Registry
Received 30 September 2019
Accepted for publication 12 May 2020
Published 19 June 2020 Volume 2020:12 Pages 651—657
Checked for plagiarism Yes
Review by Single-blind
Peer reviewer comments 2
Editor who approved publication: Professor Henrik Toft Sørensen
Mattias Hedegaard Kristensen,1 Sigrun Alba Johannesdottir Schmidt,2 Line Kibsgaard,1 Hanne Hove,3 Mette Sommerlund,1 Uffe Koppelhus1
1Department of Dermatology, Aarhus University Hospital, Aarhus, Denmark; 2Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark; 3Centre for Rare Diseases, Copenhagen University Hospital, Copenhagen, Denmark
Correspondence: Uffe Koppelhus
Department of Dermatology, Aarhus University Hospital, F3, Plan 2,202,Palle Juul-Jensens Boulevard 99, DK 8200, Denmark
Tel +45 2494 6245
Fax +45 7846 1860
Purpose: Inherited ichthyosis is a monogenetic disease characterized by hyperkeratosis and scaling of the skin, with large interindividual variation in severity. It can affect quality of life for patients and their families. Population-based data on inherited ichthyosis are lacking, which hampers studies into its epidemiology.
Patients and Methods: Based on medical record review, we validated diagnoses of inherited ichthyosis in two nationwide population-based registries commonly used for epidemiological research: The Danish National Patient Registry and the Danish Pathology Registry. The study period was January 1, 1977, through December 31, 2015. Validation samples were taken from one regional hospital without a specialized dermatological department and two specialized dermatological departments. Positive predictive values (PPVs) were estimated overall and for each coding system (ICD-8, ICD-10 and SNOMED), including for specific ICD-10 codes.
Results: We identified 1772 first-time diagnoses of inherited ichthyosis; 363 patients were diagnosed at the departments selected for validation, and 307 of these patients (84.6%) had medical records enabling validation. We observed an overall PPV of 73.3% (95% CI: 68.1– 77.9). For ICD-8, ICD-10, and SNOMED diagnoses, the PPVs were 73.2% (95% CI: 58.1– 84.3), 74.7% (95% CI: 69.0– 79.7), and 46.2% (95% CI: 22.1– 71.7), respectively. In analyses for ICD-10 diagnoses, we observed much higher validity of diagnoses from the specialized departments (PPV 79.7%; 95% CI: 74.1– 84.3) than the regional hospital (PPV 5.9%; 95% CI: 0.6– 24.3). The PPVs for specific diagnoses were 80.1% for ichthyosis vulgaris and 96.6% for X-linked ichthyosis but below 45% for remaining, rarer, subtypes.
Conclusion: The PPV of first-time diagnosis of inherited ichthyosis made at specialized dermatological departments in the Danish National Patient Registry is approximately 80%. Diagnoses from the Danish Pathology Registry had low PPVs precluding their use for research.
Keywords: Denmark, diagnosis, ichthyosis, health administrative data, registration, validity
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