Associations Between Serum Uric Acid,Excretion Of Uric Acid And Kidney Stones,Simple Renal Cysts

Objectives With the changes of lifestyle and diet,the prevalence of hyperuricemia and gout increased year by year.Hyperuricemia and gout can lead to damage in multiple target organs,such as kidneys.Previous studies suggested that high level of serum uric acid could increase the risk of kidney stones.Any relationship between excretion of uric acid and kidney stones remains controversial.In previous studies,the excretion of uric acid was assessed by total 24-h urinary uric acid values,which affected by serum uric acid level,urine volume and so on.Fractional excretion of uric acid(FEUA)could better reflect the association between uric acid excretion and kidney stones.It was reported that hyperuricemia,gout were associated with simple renal cysts in univariate analysis.What about the associations in multivariate analysis? The relationship between excretion of uric acid and simple renal cysts has not been reported.In addition,renal damage was an important complication of type 2 diabetes.Uric acid metabolism in diabetic patients was different from healthy individuals.What about the above-mentioned relationship in type 2 diabetes? Therefore,the objectives of our studies were to:(1)investigate the associations between serum uric acid and kidney stones,simple renal cysts in healthy subjects,type 2 diabetes and gout patients;(2)explore the relationships between gout and kidney stones,simple renal cysts;(3)analyze the connection of excretion of uric acid to kidney stones and simple renal cysts in type 2 diabetes and gout patients.MethodsWe performed two cross-sectional studies in healthy subjects and in type 2 diabetic patients,respectively.And we conducted a case-control study of men and postmenopausal women with gout and sex-and age-matched controls.After history-taking,physical examination,laboratory investigation and ultrasound were performed,data was recorded,organized and then analyzed by SPSS 20.0.The continuous variables of normal distribution were expressed as mean±SD and compared by the Student’s t test.The non-normal distribution variables were expressed as and median(interquartile range 25-75%)and compared by the Mann-Whitney U test.The categorical variables were expressed as percentages and compared by the Chi-square test.The binary Logistic regression analysis was used to determine the risk factors of the disease and investigate the adjusted odd ratio of the association between factors and disease.Results(1)In healthy subjects,the prevalence of kidney stones in group with serum uric acid level > 480μmol/L was significantly higher than that in groups with serum uric acid level ≤300μmol/L,300-360μmol/L and 360-420μmol/L(15.4% vs.3.8%,3.9%,5.6%,all Pvalues < 0.01).Compared with group with serum uric acid level ≤300μmol/L,the multivariate-adjusted risk ratio of kidney stones for group with serum uric acid level > 480μmol/L was 2.96 [95% CI(95% confidence interval)1.01-8.69].The prevalence of simple renal cysts in groups with serum uric acid level 360-420μmol/L,420-480μmol/L,>480μmol/L was significantly higher than that in groups with serum uric acid level ≤300μmol/L and 300-360μmol/L(13.9%,14.2%,12.3% vs.4.6%,5.4%,all P-values < 0.05).However,multivariate-adjusted associations indicated a nonsignificant relationship between serum uric acid and simple renal cysts.(2)In type 2 diabetic patients,the prevalence of kidney stones in group with serum uric acid level > 420μmol/L was significantly higher than that in group with serum uric acid level ≤300μmol/L(14.2% vs.9.8%,P < 0.01).Moreover,hyperuricemia was an independent risk factor of kidney stones [OR(odd ratio)=1.44,95% CI 1.03-2.00)].When the patients were grouped into three tertiles on the basis of their FEUA,there was no significant difference in the prevalence of kidney stones among the three groups.The prevalence of simple renal cysts in group with serum uric acid level >420μmol/L was significantly higher than that in groups with serum uric acid level ≤300μmol/L and 300-420μmol/L(23.8% vs.16.0%,16.9%,both P-values < 0.01).However,hyperuricemia was not an independent risk factor for simple renal cysts.When the patients were grouped into three tertiles on the basis of their FEUA,the prevalence of simple renal cysts was higher in high tertile than in low tertile(18.0% vs.14.3%,P<0.05).Furthermore,high tertile of FEUA was an independent risk factor of simple renal cysts(OR =1.36,95%CI 1.05-1.78).(3)In case-control study,the prevalence of kidney stones was significantly higher in gout patients than that in controls(29.5% vs.5.1%,P<0.001).Kidney stones independently increased the risk of gout(OR=6.53,95%CI 3.89-10.95).The risk of gout in patients with two or more stones(OR=9.50,95%CI 4.13-21.88)was higher than that in patients with only one stone(OR=4.69,95%CI 2.34-9.40).Similarly,the prevalence of simple renal cysts was significantly higher in gout patients than that in controls(21.6% vs.7.9%,P<0.001).Simple renal cysts independently increased the risk of gout(OR=2.34,95%CI 1.46-3.75).The risk of gout was even higher in patients with two or more cysts(OR=6.94,95%CI 2.63-18.31).(4)In men and postmenopausal women with gout,the prevalence of kidney stones in group with serum uric acid level > 540μmol/L was significantly higher than that in groups with serum uric acid level ≤480μmol/L and 480-540μmol/L(36.9% vs.20.2%,24.8%,both P-values < 0.05).FEUA still has nothing to do with kidney stones.There was no significant difference in the prevalence of simple renal cysts among groups with different serum uric acid level.When the patients were grouped into three tertiles on the basis of their FEUA,the prevalence of simple renal cysts was significantly higher in high tertile and middle tertile than in low tertile(25.8%,26.5% vs.13.0%,both P-values < 0.05).Conclusions(1)In healthy subjects,type 2 diabetes and gout-control subjects,high level of serum uric acid was independently associated with kidney stones.FEUA has nothing to do with kidney stones.(2)In healthy subjects and type 2 diabetes,there was a positive but not significant connection between hyperuricemia and simple renal cysts.In case-control study,gout independently increased the risk of simple renal cysts.(3)In type 2 diabetes,high excretion of uric acid was independently associated with simple renal cysts.In gout patients,there was also a positive connection between high excretion of uric acid and simple renal cysts.