No diagnostic utility of antibody patterns against <i>Klebsiella pneumoniae</i> capsular serotypes in patients with axial spondyloarthritis vs. patients with non-specific low back pain: a cross-sectional study

<b>Objectives</b>: To investigate whether antibody response patterns against <i>Klebsiella pneumoniae</i> capsular serotypes can discriminate patients with axial spondyloarthritis (axSpA) from patients with non-specific low back pain (LBP). <b>Method</b>: Immunoglobulin (Ig)G and IgA antibodies against <i>K. pneumoniae</i> capsular serotypes K2, K26, K36, and K50 were measured, and antibody seropositivity compared between groups and analysed for patient correlation in five different groups: (a) 96 patients fulfilling the Assessment of SpondyloArthritis International Society (ASAS) classification criteria for axSpA; (b) 38 patients with either a positive magnetic resonance imaging (MRI) scan as defined by ASAS or a positive human leucocyte antigen (HLA)-B27 status plus one clinical SpA feature, characterized as ‘non-axSpA’; (c) 82 non-specific LBP patients; (d) 40 healthy blood donors and (e) 43 patients with diagnosed ankylosing spondylitis (AS) served as the negative and positive control groups. <b>Results</b>: There was no difference in IgG and IgA seropositivity against all serotypes between the axSpA, non-axSpA, and LBP groups. No significant correlations were found between anti-<i>Klebsiella</i> antibodies and age, gender, HLA-B27, or high-sensitivity C-reactive protein (hsCRP). IgG seropositivity against K50 was more frequent in AS (25.6%) than in axSpA (13.5%, p <b>Conclusions</b>: The antibody patterns against <i>K. pneumoniae</i> serotypes K2, K26, K36, and K50 did not discriminate between early axSpA and non-specific LBP.