Background Urolithiasis greatly impact urate lowering therapy in Chinese gout patients. Benzbromarone is contraindicated and Chinese is high risk of allopurinol hypersensitivity syndrome. Febuxostat is too expensive for many patients. Few study about urolithiasis in Chinese gout patients are presented.

Objectives To investigate the prevalence and risk factors of urolithiasis in south Chinese gout patients.

Methods Patients with primary gout were recruited in the present cross-section study. Urolithiasis was defined as positive stone history and/or ultrasonography. All inpatients with estimated glomerular filtration rate (eGFR) over 30 ml/min/1.73 m² underwent 24 hours urinary chemistry assay including uric acid (UA), UA concentration, clearance of UA, Cr, calcium, phosphorus, potassium, sodium and chloride. Logistic regression were performed to examine association of urolithiasis with independent variables including age, gender, duration of gout, sUA, previous urate lowering therapy, serum creatinine, eGFR, body mass index, urine pH and 24 hours urinary chemistry assay.

Results (1) Two hundred and nighty-four patients were recruited. Mean age of male (N=255) and female (N=39) were 54.4±16.4 and 67.2±15.3, respectively. Average serum UA was 9.0±2.5mg/dl and 25.9% of patients presented tophi. Allopurinol, benzbromarone, or a combination of these two drugs had been prescribed in 97 patients (33.0%), 18 patients (6.1%) and 36 patients (12.2%), respectively. The rest 143 patients (48.6%) had not received urate lowering therapy before. (2) One hundred and eleven gout patients (37.8%) complicated with urolithiasis and urolithiasis was observed in 69 of them (62.1%) on ultrasonography. Compared with non urolithiasis group, urolithiasis group had significant higher serum creatinine (1.6±0.6 VS 1.3±0.3 mg/dl], lower eGFR (56.3±18.0 VS 64.1±18.4 ml/min/1.73m²) and higher alcohol overuse (38.7% VS 26.2%) (P<0.05). (3) Among 102 patients performed 24 hours urinary chemical assay, 45 patients complicated with urolithiasis. Urolithiasis group had significantly higher 24 hours urine UA concentration than non-urolithiasis group (30.4±13.1 VS 23.9±11.9 mg/dl, P=0.01). There were no significant difference of other variables between two groups. Prevalence of urolithiasis increased significantly across increasing quartiles of urinary UA concentration (P=0.012, Table 1). (4) Logistic regression suggested that risk factors of urolithiasis were urinary UA concentration grouped by quartile (P=0.05) and urinary calcium excretion [OR 1.26 (1.01, 1.57), P=0.04]. Urinary UA concentration over 24.4mg/dl was associated with increasing risk of urolithiasis (Table 1).

Conclusions Prevalence of urolithiasis in Chinese gout patients were high and predicted by excess urinary UA concentration and urinary calcium excretion.

Acknowledgement The present study was supported by Guangdong Natural Science Foundation, China (Grant no. 2014A030310086) to Qian-Hua Li.

Disclosure of Interest None declared