Higher Serum Uric Acid Levels Protect Against Osteoporosis in Patients With Axial Spondyloarthropathy
Gillian Fitzgerald (1,2), Tochukwu Anachebe (1), Ronan Mullan (3), David Kane (3), Kevin McCarroll (4), Finbar O’ Shea (1).
(1) Department of Rheumatology, St. James’s Hospital. (2) Department of Medicine, Trinity College Dublin (3) Department of Rheumatology, Tallaght University Hospital (4) Department of Medicine for the Elderly, St. James’s Hospital.
Serum urate (SUA) is a risk factor for metabolic disease, such as hypertension. SUA also has an antioxidant effect, protecting against diseases with high oxidative stress. Osteoporosis is characterised by high oxidative stress levels, mediated through increased osteoclastic activity. Antioxidants may have protective properties against bone loss. Literature examining SUA and its impact on bone mineral density (BMD) in axial spondyloarthropathy (axSpA) is limited.
Aim: examine the relationship between SUA and BMD in a well-characterised axSpA cohort.
Patients fulfilling modified New York (mNY) or Assessment of SpondyloArthritis International Society (ASAS) criteria were consecutively recruited from 2 centres in this cross-sectional study. Patients underwent a detailed assessment: demographics, disease-related variables (validated measures of disease activity included BASDAI, ASDAS-CRP, BASMI), clinical examination, laboratory parameters (routine bloods, SUA, CRP, vitamin D). BMD was assessed using dual-energy x-ray absorptiometry of the lumbar spine and hip (total hip and femoral neck). SUA >360 µmol/L was considered high. Analysis was performed using SPSS.
In total, 107 patients were included: 76% male, median (IQR) age 51.5 (17.8) years, disease duration 23.5 (20.4) years. Median BMI was 27.6 (6.5) kg/m^2 (31% obese). Low BMD was present in 38.5% of the cohort. Median (IQR) SUA in the cohort was 312 (119) µmol/L. SUA >360 µmol/L was present in 34% (n=36). More men than women had high SUA (94% v 5.6%, p<0.01). BMI was higher in those patients with SUA above 360 µmol/L than patients with normal levels (mean difference 4.2 kg/m^2, 95% CI 2.1-6.3).
SUA correlated positively (p<0.01) with BMD at the spine (r=0.3) and total hip (r=0.3). Patients with a high SUA had significantly less osteopenia or osteoporosis (19%) than patients with a normal SUA (46%) (OR 3.5, 95% CI 1.4-9.3).
In univariate logistic regression analysis, low SUA and low BMI were associated with low BMD. After correcting for obesity, patients with high SUA remained independently associated with normal BMD compared to those patients with a normal SUA (OR 3.4, 95% CI 1.2-9.6).
High SUA levels are independently associated with normal BMD, suggesting a protective effect of SUA against osteoporosis in axSpA patients.