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Table 1 Characteristics of studies included in the present systematic review and meta-analysis. HS hidradenitis suppurativa, n number of cases, ICD-10 10th revision of the International Statistical Classification of Diseases and Related Health Problems, SNOMED CT SNOMED Clinical Terms

From: Hidradenitis suppurativa and acne vulgaris and conglobata—systematic review and meta-analysis

AuthorYearStudy periodCountryDesignn (HS)n (controls)Data sourceSelection of HS casesSelection of controlsMatchingMean age (years)Females (%)
Ingram20182013UKRetrospective case-control69,842 (proxy)93,869Clinical Practice Research Datalink (CPRD)Proxy cases: Based on clinical features and algorithm, confirmed by validation questionnaireGeneral population participants in the database without diagnosis of HS1: 1 matched based on age, sex and registration at the same primary care practice, obesity, diabetes, smoking, comorbidities
     24,027 (physician-diagnosed)93,869Clinical Practice Research Datalink (CPRD)Physician diagnosed cases: Codes M25y100 (hidradenitis) and M25y111 (hidradenitis suppurativa)General population participants in the database without diagnosis of HS1: 1 matched based on age, sex and registration at the same primary care practice, obesity, diabetes, smoking, comorbidities
Kimball20181999–2014USARetrospective case-control2292 (mild HS)2292OptumHealth Care Solutions, Inc. databaseAt least two diagnoses for HS (ICD-9 code 705.83) recorded on different dates between January 1999 and March 2014Database participants over the same study period without diagnosis for HS1:1 matching based on age, sex, region of residence, healthcare plan42.19 vs 42.1974 vs 74
     3065 (severe HS)3065OptumHealth Care Solutions, Inc. databaseHS severity based on predetermined clinical characteristicsDatabase participants over the same study period without diagnosis for HS1:1 matching based on age, sex, region of residence, healthcare plan42.19 vs 42.1971 vs 71
Lee20182007–2016KoreaRetrospective case-control28,516142,580Korean National Institute of Health databaseDiagnosed by ICD-10 code I.729 between January 2007 and December 2016Random selection of patients from a database without diagnosis of HS1:5 matching based on age and sex. Adjustment for age, sex, socioeconomic status, diabetes, hypertension, hyperlipidaemia33.6 vs 33.638.7 vs 38.7
Wertenteil20182012–2017USARetrospective case-control48,05016,899,470Explorys developed by International Business Machines (IBM) CorporationSNOMED-CT term “hidradenitis”, which has one-to-one mapping with the ICD-9 code for hidradenitis (705.83)Database participants without diagnosis for HSAdjustment for age, sex, obesity, smoking status, PCOS status18-44y: 60 vs 39.6; 45-64y: 30.1 vs 33; ≥65y: 9.8 vs 27.474.4 vs 56.5