SAT0302 Spinal involvement in axial psoriatic artritis is not determined by the presence of HLA-B27. Is the HLA-B27 arm of the axial SPA criteria reliable for classifying axial psoriatic arthritis?

Background There is a debate whether axial psoriatic arthritis (axPsA) is an ankylosing spondylitis with psoriasis, however due to the fact that PsA has characteristic clinical features, this concept is debatable. On the other hand HLA-B27 is a key component of the clinical arm of the new ASAS criteria for axial SpA Objectives To determine the prevalence of HLA-B27 in PsA and to analyze its prevalence according to the clinical forms Methods Cross-sectional prevalence study of HLA-B27. HLA-B27 was determined in the following populations: a) healthy controls (HC) (n=308) and AS (n=106) (1), b) cutaneous psoriasis (n=113), c) PsA (n=172). axPsA was defined according to our previous definition (2,3). HLA-B27 was determined wit a commercial kit: Invitrogen®, Allset Gold B27 Low and High Res SSP. For each group of patients, HLA-B27 prevalence was determined, together with its 95% confidence interval. Using data from the Galician population as reference, prevalence ratio and odds ratio values were estimated from a logistic regression model. Comparisons among groups were performed by using the Mann-Whitney U, chi-squared and Fisher’s exact tests. Results The prevalence of HLA-B27 was: HC 9,4%, AS 94,3% (p