title: Is HLA-B27 increased in patients diagnosed with undifferentiated arthritis? Results from the Leiden early arthritis cohort.
abstract: OBJECTIVE
  Undifferentiated arthritis (UA) is a common form of arthritis. According to the Assessment of Spondyloarthritis international Society (ASAS) criteria for peripheral spondyloarthritis (pSpA), HLA-B27 can be used to help classify patients with pSpA. We tested whether HLA-B27 is increased in patients diagnosed with UA.
  
  
  METHODS
  Prevalence of HLA-B27 was compared between healthy controls and patients with UA. SpA features were compared between HLA-B27-positive and -negative UA, and SpA.
  
  
  RESULTS
  We found 10.1% of UA (38/375) versus 7.2% (403/5584) of controls were HLA-B27-positive (OR 1.5, 95% CI 1.0-2.1; p = 0.037). HLA-B27-positive patients with UA had more SpA features than HLA-B27-negative patients (mean 1.6, SD 1.0, and 0.9 SD 0.6; p < 0.001), but patients with SpA had significantly more SpA features (mean 4.5, SD 1.5; p < 0.001). Family history and preceding infection were features more common in HLA-B27-positive than in HLA-B27-negative UA (15.8% vs 1.3%, p = 0.04 and 15.8% vs 2.6%, p = 0.04). After HLA-B27 testing, 21 additional patients (5.6%) with UA could potentially have been classified with pSpA according to the ASAS criteria.
  
  
  CONCLUSIONS
  HLA-B27 is more common in patients with UA than in controls. However, the yield of HLA-B27 testing in UA is low. Our results suggest that HLA-B27 testing should be reserved for patients with additional SpA features.
authors.affiliation: From the Department of Rheumatology, Leiden University Medical Centre, Leiden, the Netherlands.F. van Gaalen, MD, PhD; R. van den Berg, MSc; I. Verhoog, BSc; J. Schonkeren, BSc; A. van der Helm-van Mil, MD, PhD; T. Huizinga, MD, PhD; D.M. van der Heijde, MD, PhD, Department of Rheumatology, Leiden University Medical Centre. f.a.van_gaalen@lumc.nl.
authors.forename: Floris
authors.initials: F
authors.lastname: van Gaalen
authors.affiliation: From the Department of Rheumatology, Leiden University Medical Centre, Leiden, the Netherlands.F. van Gaalen, MD, PhD; R. van den Berg, MSc; I. Verhoog, BSc; J. Schonkeren, BSc; A. van der Helm-van Mil, MD, PhD; T. Huizinga, MD, PhD; D.M. van der Heijde, MD, PhD, Department of Rheumatology, Leiden University Medical Centre.
authors.forename: Rosaline
authors.initials: R
authors.lastname: van den Berg
authors.affiliation: From the Department of Rheumatology, Leiden University Medical Centre, Leiden, the Netherlands.F. van Gaalen, MD, PhD; R. van den Berg, MSc; I. Verhoog, BSc; J. Schonkeren, BSc; A. van der Helm-van Mil, MD, PhD; T. Huizinga, MD, PhD; D.M. van der Heijde, MD, PhD, Department of Rheumatology, Leiden University Medical Centre.
authors.forename: Inge
authors.initials: I
authors.lastname: Verhoog
authors.affiliation: From the Department of Rheumatology, Leiden University Medical Centre, Leiden, the Netherlands.F. van Gaalen, MD, PhD; R. van den Berg, MSc; I. Verhoog, BSc; J. Schonkeren, BSc; A. van der Helm-van Mil, MD, PhD; T. Huizinga, MD, PhD; D.M. van der Heijde, MD, PhD, Department of Rheumatology, Leiden University Medical Centre.
authors.forename: Joris
authors.initials: J
authors.lastname: Schonkeren
authors.affiliation: From the Department of Rheumatology, Leiden University Medical Centre, Leiden, the Netherlands.F. van Gaalen, MD, PhD; R. van den Berg, MSc; I. Verhoog, BSc; J. Schonkeren, BSc; A. van der Helm-van Mil, MD, PhD; T. Huizinga, MD, PhD; D.M. van der Heijde, MD, PhD, Department of Rheumatology, Leiden University Medical Centre.
authors.forename: Annette
authors.initials: A
authors.lastname: van der Helm-van Mil
authors.affiliation: From the Department of Rheumatology, Leiden University Medical Centre, Leiden, the Netherlands.F. van Gaalen, MD, PhD; R. van den Berg, MSc; I. Verhoog, BSc; J. Schonkeren, BSc; A. van der Helm-van Mil, MD, PhD; T. Huizinga, MD, PhD; D.M. van der Heijde, MD, PhD, Department of Rheumatology, Leiden University Medical Centre.
authors.forename: Tom
authors.initials: T
authors.lastname: Huizinga
authors.affiliation: From the Department of Rheumatology, Leiden University Medical Centre, Leiden, the Netherlands.F. van Gaalen, MD, PhD; R. van den Berg, MSc; I. Verhoog, BSc; J. Schonkeren, BSc; A. van der Helm-van Mil, MD, PhD; T. Huizinga, MD, PhD; D.M. van der Heijde, MD, PhD, Department of Rheumatology, Leiden University Medical Centre.
authors.forename: Désirée M
authors.initials: DM
authors.lastname: van der Heijde
mesh_terms: D000328:Adult; D000368:Aged; D001168:Arthritis / Q000097:blood*; D005260:Female; D015796:HLA-B27 Antigen / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D025241:Spondylarthritis / Q000097:blood / Q000175:diagnosis*
chemical_list: D015796:HLA-B27 Antigen
keywords: GENETIC RISK FACTORS; HLA-B27; SPONDYLOARTHRITIS; UNDIFFERENTIATED ARTHRITIS