Risk factors for urolithiasis in patients with ankylosing spondylitis: a prospective case–control study

It has been reported that renal stone formation increased in patients with ankylosing spondylitis (AS). However, its reason remains unclear. The aim of this study was to evaluate serially the possible risk factors for renal stone formation in AS patients. Two groups consisted of AS patients with renal stone (n = 30), AS patients without renal stone (n = 30), and 20 healthy controls (HC) were included to the study. Parathyroid hormone, calcium, magnesium, phosphorus and immunoglobulin A levels and 24 h urine were evaluated at baseline, and three times monthly. Serum calcium levels were higher in AS patients with urolithiasis than those without at baseline and third-month evaluation (baseline: 9.53 ± 0.3 vs 9.32 ± 0.3 mg/dl; p < 0.03; at third-month evaluation: 9.74 ± 0.2 vs 9.56 ± 0.3 mg/dl; p < 0.01). No significant differences were found between groups in terms of PTH and magnesium levels. In all evaluation times, although urinary calcium excretion was higher in AS patients with urolithiasis than in those without, it did not reach a statistical significance. IgA levels were significantly higher in renal stone sufferers than HC patients in all evaluation times.AS patients with urolithiasis also had high IgA levels compared with AS patients without renal stone at the second-month evaluation time (276 ± 102 vs 219 ± 104 mg/dl, p < 0.002). Increased levels of serum calcium and IgA levels as well as family history for urolithiasis may be an indicator of the development of urolithiasis in AS patients.