Baseline Analysis Of The Database Of Ankylosing Spondylitis In China

Part I Baseline analysis of the database of ankylosing spondylitisObjective:The aim of this study was to set up a large, longitudinal and prospective database to investigate the diagnosis, prognosis, epidemiology, and pathogenesis of ankylosing spondylitis in Chinese population.Methods:Consecutive 449 outpatients with confirmed ankylosing spondylitis (AS) were recruited without further inclusion restrictions and followed annually. Characteristics of registration and demography (age, gender, date at onset of back pain, date of diagnosis, presence of AS features, family history) and the current condition (disease activity, severity, treatments, laboratory tests) were collected at the clinic by rheumatologists.Results:449 patients (mean age:29.4±8.5 years, female 84.0%, HLA-B27 positive 81.2%) were included in the analysis. In this cross-sectional analysis we only used data at the first visit (from May 2014 to December 2014).The 3 groups did not differ in the frequency of gender, HLA-B27 positivity, family history positivity, arthritis, enthesitis, inflammatory bowel disease (IBD), psoriasis, and abnormal CRP. More patients with longer duration had pain located in the thoracic spine (P＝0.003), a higher prevalence of anterior chest wall (ACW, p=0.024) and uveitis (P<0.001).Conclusion:This large cohort should improve our knowledge on the characteristics, pathogenesis and natural history of ankylosing spondylitis in China.Part Ⅱ Calculating the ankylosing spondylitis disease activity score when the c-reactive protein level is below the limit of detectionObjective:To calculating the ankylosing spondylitis disease activity score (ASDAS), the most widely used activity score in ankylosing spondylitis (AS), when the C-reactive protein (CRP) level is below the limit of detection.Methods:A total of 386 patients with AS were included and divided into 2 groups with CRP≥3.5 mg/L (n= 266) and CRP<3.5 mg/L(n=120). Patient with a CRP level below the limit of detection (3.5 mg/L) were selected to calculate the ASDAS-CRP with different imputations (range 0-3.5 mg/L, at 0.5mg/L intervals and range 1-2 mg/L, at 0.1 mg/L intervals). Three methods were used to test the agreement between ASDAS-CRP and ASDAS-erythrocyte sedimentation rate (ESR).Results:The ASDAS-CRP showed good correlation with the ASDAS-ESR when the CRP was≤3.5 mg/L (r= 0.899). The ASDAS-ESR showed better agreement with the ASDAS-CRP using the CRP imputation values of 1.5mg/L.Conclusions:There is good agreement between the ASDAS-CRP and ASDAS-ESR. When the CRP level is below the limit of detection,1.5 mg/L should be used to calculate the ASDAS-CRP score.