Increased serum alkaline phosphatase levels correlate with high disease activity and low bone mineral density in patients with axial spondyloarthritis

Objectives: Recent studies report an association between serum alkaline phosphatase (ALP) levels and inflammation. The present study examined the relationship between ALP and disease activity, bone mineral density (BMD), and radiological damage in axial spondyloarthritis (SpA). Methods: A total of 115 patients who fulfilled the ASAS axial SpA criteria were enrolled. Serum ALP, bone-specific ALP (BALP), serum cross-linked telopeptide of type-I collagen (sCTX), and inflammatory markers were measured. Clinical parameters, BMD, grade of sacroiliitis, and the modified Stoke AS Spinal Score (mSASSS) were also assessed. The Ankylosing Spondylitis Disease Activity Score (ASDAS) was also calculated. The associations between serum ALP, disease activity score, BMD, and radiologic damage were evaluated. Results: The mean serum ALP level was 77 ± 26. U/l. Serum ALP levels increased in 14 patients (13%). Serum ALP levels increased along with ASDAS-CRP after adjusting for age and sex (. p = 0.004), and were significantly correlated with ASDAS-ESR and ASDAS-CRP (. p = 0.001 and p < 0.001, respectively), negatively correlated with BMD in the lumbar spine and femoral neck (. p = 0.003 and 0.046, respectively), and positively correlated with sacroiliitis grade and the mSASSS (. p < 0.001 and p < 0.002, respectively). BALP and sCTX were not associated with disease activity or BMD. Multivariate analysis showed that serum ALP was independently associated with ASDAS-CRP (. p = 0.010). Conclusions: Increased serum ALP levels were associated with high disease activity, low BMD, and higher structural damage scores in SpA patients.