title: Does body mass index (BMI) influence the Ankylosing Spondylitis Disease Activity Score in axial spondyloarthritis?: Data from the SPACE cohort.
abstract: OBJECTIVE
  Obesity is associated with elevated C reactive protein (CRP) levels. The Ankylosing Spondylitis Disease Activity Score (ASDAS) combines patient-reported outcomes (PROs) and CRP. We evaluated the effect of body mass index (BMI) on CRP and on ASDAS, and studied if ASDAS can be used in obese axial spondyloarthritis (axSpA) patients to assess disease activity.
  
  
  METHODS
  Baseline data of patients with chronic back pain of short duration included in the SPondyloArthritis Caught Early (SPACE) cohort were used. Collected data included BMI and ASDAS. Patients were classified according to the ASAS axSpA classification criteria and BMI (overweight ≥25 and obese ≥30). Correlation and linear regression analyses were performed to assess the relation between BMI and ASDAS. Linear regression models were performed to assess if age or gender were effect modifiers in the relation between BMI and CRP, and between BMI and ASDAS.
  
  
  RESULTS
  In total, 428 patients were analysed (n=168 axSpA; n=260 no-axSpA). The mean age was 31.1 years, 36.9% were male, 26.4% were overweight and 13.3% obese, median CRP was 3 mg/L and the mean ASDAS was 2.6. Gender was the only factor modifying the relationship between BMI and CRP as BMI had an influence on CRP only in females (β=0.35; p<0.001). Correlations between BMI and CRP or PROs were generally weak, and only significant for CRP in female patients. BMI was not related to ASDAS in axSpA patients.
  
  
  CONCLUSIONS
  ASDAS is not affected by BMI in axSpA patients. Therefore, based on our data it is not necessary to take BMI in consideration when assessing disease activity using ASDAS in axSpA patients.
authors.affiliation: Department of Rheumatology , Leiden University Medical Center , Leiden , The Netherlands.
authors.forename: Roxana
authors.initials: R
authors.lastname: Rubio Vargas
authors.affiliation: Department of Rheumatology , Leiden University Medical Center , Leiden , The Netherlands.
authors.forename: Rosaline
authors.initials: R
authors.lastname: van den Berg
authors.affiliation: Department of Rheumatology , Leiden University Medical Center , Leiden , The Netherlands.
authors.forename: Miranda
authors.initials: M
authors.lastname: van Lunteren
authors.affiliation: Department of Rheumatology , Leiden University Medical Center , Leiden , The Netherlands.
authors.forename: Zineb
authors.initials: Z
authors.lastname: Ez-Zaitouni
authors.affiliation: Department of Rheumatology , Leiden University Medical Center , Leiden , The Netherlands.
authors.forename: Pauline A C
authors.initials: PA
authors.lastname: Bakker
authors.affiliation: Department of Rheumatology , Diakonhjemmet Hospital , Oslo , Norway.
authors.forename: Hanne
authors.initials: H
authors.lastname: Dagfinrud
authors.affiliation: Rheumatology Unit, Department of Medicine DIMED , University of Padova , Italy.
authors.forename: Roberta
authors.initials: R
authors.lastname: Ramonda
authors.affiliation: Department of Rheumatology, Amsterdam Medical Center, Amsterdam, The Netherlands; Atrium Medical Center, Heerlen, The Netherlands.
authors.forename: Robert
authors.initials: R
authors.lastname: Landewé
authors.affiliation: Department of Rheumatology , Groene Hart Ziekenhuis , Gouda , The Netherlands.
authors.forename: Esmeralda
authors.initials: E
authors.lastname: Molenaar
authors.affiliation: Department of Rheumatology , Leiden University Medical Center , Leiden , The Netherlands.
authors.forename: Floris A
authors.initials: FA
authors.lastname: van Gaalen
authors.affiliation: Department of Rheumatology , Leiden University Medical Center , Leiden , The Netherlands.
authors.forename: Désirée
authors.initials: D
authors.lastname: van der Heijde
keywords: Ankylosing Spondylitis; Disease Activity; Spondyloarthritis