Table 1.

Algorithm used to define different rheumatic and/or inflammatory conditions in the cases and in their first-grade relatives

Group of conditions	ICD10 codes	Criteria	Exclusion criteria
Seropositive RA	M05, M08.0	Two or more visits, with at least one with specialist at a department of internal medicine or rheumatology
Seronegative RA	M06, M08.3	Two or more visits, with at least one with specialist at a department of internal medicine or rheumatology	Seropositive RA
JIA	M08.2, M08.4, M08.8, M08.9	Two or more visits before age 18, or two or more visits, with at least one with specialist at a department of internal medicine or rheumatology	Seropositive or seronegative RA
Other inflammatory arthritis	M13	Any visit	Seropositive/negative RA or JIA
Spondyloarthropathies*	M45, M46, M02, M03, M07.4-6, M08.1, K50, K51, H20	Any visit
Psoriasis /psoriatic arthritis	M07.0-3, L40, M09	ICD code L40 counted only if recorded at dermatology, internal medicine or rheumatology departments
Lupust	M32, L93	Two or more visits, with at least one with specialist at a department of internal medicine, rheumatology or nephrology
Connective tissue disease‡	M33, M34, M35.0, M35.1, K73.2	Two or more visits, with at least one with specialist at a department of internal medicine, rheumatology or nephrology
Arthralgia	M25.5	Any visit	If any diagnosis falling in any other group
Osteoarthritis	M15, M16, M17, M18, M19	Any visit	If any diagnosis falling in any other group

^*Ankylosing spondylitis, spondyloarthritis unspecified, reactive arthritis, juvenile spondyloarthritis, enteropathic arthritis/spondylitis, uveitis, Crohn’s disease and ulcerative colitis.

^†Systemic and/or discoid lupus erythematosus.

^‡Dermatomyositis, polymyositis, systemic sclerosis, Sjögren’s syndrome and autoimmune hepatitis.

ICD10, International Classification of Diseases tenth revision; JIA, juvenile idiopathic arthritis; RA rheumatoid arthritis.