title: Factors associated with the decision of the rheumatologist to order sacroiliac joints magnetic resonance imaging (SI-MRI) or HLA-B27 testing in the diagnostic work-up of patients with spondyloarthritis in clinical practice.
abstract: OBJECTIVE
  To evaluate the patients' characteristics associated with the clinical decision to request SI-MRI and/or HLA-B27 in patients with SpA in daily practice.
  
  
  METHODS
  Patients referred to a rheumatology outpatient-clinic in a national referral-centre were selected. Patients with a clinical diagnosis of SpA according to the rheumatologist were included. SI-MRI and HLA-B27 was available for patients in whom the rheumatologists had ordered these tests. Characteristics associated with ordering SI-MRI or HLA-B27 were identified with univariable analyses. Variables with p-value <0.05 and >80% completeness were selected for further analysis. A multivariable logistic regression analysis was used to evaluate the determinants related with the decision to perform SI-MRI and/or HLA-B27 and odds ratios with 95% confidence intervals were calculated.
  
  
  RESULTS
  In total, 581 patients with SpA were included in the cohort, 72% were men, mean age 34.6±12.1 and disease duration 7.3±9.7 years. Of these patients, 24% (n=137) had SI-MRI and 77% (n=441) had HLA-B27 tests ordered. Independently predictive factors for ordering a SI-MRI were the presence of IBP (OR=1.81), enthesitis (OR=1.57) and the number of initial-symptoms at presentation (OR=1.27 per additional symptom present). Independently predictive factors of HLA-B27 testing were the number of initial-symptoms (OR=1.45 per symptom) and uveitis (OR=3.19).
  
  
  CONCLUSIONS
  This study strongly suggests that rheumatologists use certain clinical clues to decide if they order expensive and scarce tests in the diagnostic work-up of SpA patients. These manifestations may increase the efficiency of these tests in clinical practice and suggest that clinical reasoning follows principles of Bayesian theory.
authors: Rheumatology Department, Leiden University Medical Center, Leiden, The Netherlands; and Rheumatology Department, School of Medicine, HMC/UMNG, Bogotá, Colombia. wilson.bautista@gmail.com.
authors: Wilson
authors: W
authors: Bautista-Molano
authors: Rheumatology Department, Academic Medical Center, University of Amsterdam, The Netherlands.
authors: Robert B M
authors: RB
authors: Landewé
authors: Statistics and Mathematics Department, Universidad Central, Bogotá, Colombia.
authors: Cesar
authors: C
authors: Serna
authors: Rheumatology Department, School of Medicine, HMC/UMNG, Bogotá, Colombia.
authors: Rafael
authors: R
authors: Valle-Oñate
authors: Rheumatology Department, Leiden University Medical Center, Leiden, The Netherlands.
authors: Désirée
authors: D
authors: van der Heijde
mesh_terms: D000328:Adult; D000483:Alleles; D000066491:Clinical Decision-Making; D005260:Female; D015796:HLA-B27 Antigen / Q000235:genetics*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D012446:Sacroiliac Joint / Q000000981:diagnostic imaging*; D025241:Spondylarthritis / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000235:genetics; D055815:Young Adult
chemical_list: D015796:HLA-B27 Antigen