Hyperuricemia is an independent risk factor for mortality only if chronic kidney disease is present

Serum Uric Acid and Mortality in Patients with Chronic Kidney Disease: A Systematic Review and Meta-Analysis

BACKGROUND

Existing studies suggested conflicting relationships between serum uric acid (SUA) and mortality in CKD patients. The present meta-analysis aimed to determine whether SUA can be a predictor for mortality in CKD cohorts.

METHOD

A systematical search was conducted on PubMed, EMBASE, and The Cochrane Library to identify studies reporting the relationship between SUA level and all-cause and cardiovascular mortality in CKD populations. In addition, random-effects models were adopted to calculate the hazard ratios (HRs) and corresponding 95% confidence intervals (CIs).

RESULTS

On the whole, 29 studies were involved. In the present meta-analysis, patients exhibiting the maximum SUA level showed an association with a significantly higher risk for all-cause mortality (HR, 1.30; 95% CI, 1.06-1.59) compared with patients exhibiting the minimum SUA level. As revealed from the meta-analysis of 8 studies, low level of SUA was another predictor for all-cause mortality in patients with CKD (HR, 1.36; 95% CI, 1.20-1.54). No significant relationship was identified between SUA and cardiovascular mortality.

CONCLUSIONS

Higher and lower SUA levels are both associated with significantly increased risk of all-cause mortality in patients with CKD. A appreciate dose of treatment of lowering SUA agents should be confirmed.

Hyperuricemia is associated with acute kidney injury and all-cause mortality in hospitalized patients

AIM

Hyperuricemia is a risk factor for high morbidity and mortality in several diseases. However, the relationship between uric acid (UA) and the risk of acute kidney injury (AKI) and mortality remain unresolved in hospitalized patients.

METHODS

Data from 18 444 hospitalized patients were retrospectively reviewed. The odds ratio (OR) for AKI and the hazard ratio (HR) for all-cause mortality were calculated based on the UA quartiles after adjustment for multiple variables. All analyses were performed after stratification by sex.

RESULTS

The fourth quartile group (male, UA > 6.7 mg/dL; female, UA > 5.4 mg/dL) showed a higher risk of AKI compared with the first quartile group (male, UA < 4.5 mg/dL; female, UA < 3.6 mg/dL), with the following OR: 3.2 (2.55-4.10) in males (P < 0.001); and 3.1 (2.40-4.19) in females (P < 0.001). There were more patients who did not recover from AKI in the fourth quartile compared with the first quartile, with the following OR: 2.0 (1.32-3.04) in males (P = 0.001) and 2.4 (1.43-3.96) in females (P = 0.001). The fourth quartile group had a higher risk of all-cause mortality compared with the first quartile group, with the following HR: 1.4 (1.20-1.58) in males (P < 0.001) and 1.2 (1.03-1.46) in females (P = 0.019). The in-hospital mortality risk was also higher in the fourth quartile compared with the first quartile, which was significant only in males (OR, 2.1 (1.33-3.31) (P = 0.002)).

CONCLUSION

Hyperuricemia increases the risks of AKI and all-cause mortality in hospitalized patients.

Uric acid and cardiovascular risk: What genes can say

BACKGROUND

Although the relationship of elevated serum uric acid levels and cardiovascular disease has been established in a great number of studies, the causal relevance of this finding remains ambiguous. An approach to evaluate the causal relevance of biomarkers is to exploit the natural randomised allocation of allelic variation in genes affecting their level, also known as Mendelian randomisation.

AIM

The aim of this paper is to review the current literature regarding serum uric acid levels and cardiovascular and renal disease risk in Mendelian randomisation studies.

METHODS

PubMed and Scopus databases were searched to retrieve Mendelian studies regarding uric acid, hyperuricaemia and cardiovascular risk.

CONCLUSIONS

Genetic evidence based on conventional and novel Mendelian randomisation approaches suggest a modest, if any, causal effect of serum uric acid concentration on the development of cardiovascular disease, suggesting that further study of uric acid genes is needed in order to elucidate the relationship of serum uric acid levels and cardiovascular disease.

Serum uric acid and mortality in chronic kidney disease: A systematic review and meta-analysis

BACKGROUND

Studies have shown inconsistent results about the association between serum uric acid levels and mortality in patients with chronic kidney disease (CKD).

METHODS

A systematic literature search in MEDLINE, Web of Science and bibliographies of retrieved articles was performed to identify studies investigating the association between serum uric acid and mortality in patients with CKD. Pooled hazard ratios (HR) and corresponding 95% confidence intervals (CIs) were calculated using random-effects models.

RESULTS

A total of 24 studies with 25,453 patients with CKD were included. By meta-analysis, patients with the highest serum uric acid level were associated with a significantly higher risk for mortality (14 studies; HR, 1.52; 95% CI, 1.33-1.73) compared with patients with the lowest serum uric acid level. For dose-response analysis, a linear relationship (8 studies; Pfor non-linearity=0.14) between serum uric acid levels and risk of mortality was found. Overall, an increase of 1mg/dl in serum uric acid level was associated with an 8% increased risk of mortality (21 studies; HR, 1.08; 95% CI, 1.04-1.11).

CONCLUSIONS

Elevated serum uric acid levels are significantly associated with risk of mortality in patients with CKD. Further randomized controlled trials should attempt to determine whether it improves survival to target serum uric acid in patients with CKD.

High Serum Uric Acid Levels Are Associated with All-Cause and Cardiovascular, but Not Cancer, Mortality in Elderly Adults

OBJECTIVES

To estimate the all-cause, cardiovascular, and cancer mortality risks associated with serum uric acid levels in elderly adults.

DESIGN

Cohort study.

SETTING

The Annual Geriatric Health Examination Program database from 2006 to 2010.

PATICIPANTS

Community-dwelling Taipei citizens aged 65 and older (N = 77,541).

MEASUREMENTS

Stratified according to sex, serum uric acid levels were analyzed in quartiles and as normal versus high categories. Mortality was determined by matching cohort identifications with national death files.

RESULTS

Men had significantly higher uric acid levels than women (P < .001), and mean levels increased with age (P < .001). Serum uric acid levels (normal vs high) were an independent risk factor for all-cause and cardiovascular mortality in men and women, with the strongest association found for cardiovascular mortality. The association between serum uric acid levels and cardiovascular mortality was independent of other cardiovascular risk factors such as hypertension, diabetes mellitus, hyperlipidemia, and glomerular filtration rate levels. When levels were analyzed as quartiles, men with levels in the second quartile had the lowest hazard ratios for all-cause and cardiovascular mortality.

CONCLUSION

High serum uric acid levels are associated with greater risk of all-cause and cardiovascular mortality but not cancer mortality in elderly adults. Further studies are warranted to investigate the prognostic implications and potential utility in the monitoring of therapy.

Efficacy of Febuxostat for Slowing the GFR Decline in Patients With CKD and Asymptomatic Hyperuricemia: A 6-Month, Double-Blind, Randomized, Placebo-Controlled Trial

BACKGROUND

Hyperuricemia is a putative risk factor for the progression of chronic kidney disease (CKD). We hypothesized that control of asymptomatic hyperuricemia may slow disease progression in CKD.

STUDY DESIGN

This was a single-center, double-blind, randomized, parallel-group, placebo-controlled study.

SETTING & PARTICIPANTS

Eligible participants were adults from Eastern India aged 18 to 65 years with CKD stages 3 and 4, with asymptomatic hyperuricemia.

INTERVENTION

The intervention group received febuxostat, 40mg, once daily for 6 months, while the placebo group received placebo; both groups were followed up for 6 months.

OUTCOMES

The primary outcome was the proportion of patients showing a >10% decline in estimated glomerular filtration rate (eGFR) from baseline in the febuxostat and placebo groups. Secondary outcomes included changes in eGFRs in the 2 groups from baseline and at the end of the study period.

RESULTS

45 patients in the febuxostat group and 48 in the placebo group were analyzed. Mean eGFR in the febuxostat group showed a nonsignificant increase from 31.5±13.6 (SD) to 34.7±18.1mL/min/1.73m(2) at 6 months. With placebo, mean eGFR decreased from a baseline of 32.6±11.6 to 28.2±11.5mL/min/1.73m(2) (P=0.003). The difference between groups was 6.5 (95% CI, 0.08-12.81) mL/min/1.73m(2) at 6 months (P=0.05). 17 of 45 (38%) participants in the febuxostat group had a >10% decline in eGFR over baseline compared with 26 of 48 (54%) from the placebo group (P<0.004).

LIMITATIONS

Limitations of this study included small numbers of patients and short follow-up, and ∼10% of the randomly assigned population dropped out prior to completion.

CONCLUSIONS

Febuxostat slowed the decline in eGFR in CKD stages 3 and 4 compared to placebo.

Uric Acid and Cardiovascular Events: A Mendelian Randomization Study

Obesity and diets rich in uric acid-raising components appear to account for the increased prevalence of hyperuricemia in Westernized populations. Prevalence rates of hypertension, diabetes mellitus, CKD, and cardiovascular disease are also increasing. We used Mendelian randomization to examine whether uric acid is an independent and causal cardiovascular risk factor. Serum uric acid was measured in 3315 patients of the Ludwigshafen Risk and Cardiovascular Health Study. We calculated a weighted genetic risk score (GRS) for uric acid concentration based on eight uric acid-regulating single nucleotide polymorphisms. Causal odds ratios and causal hazard ratios (HRs) were calculated using a two-stage regression estimate with the GRS as the instrumental variable to examine associations with cardiometabolic phenotypes (cross-sectional) and mortality (prospectively) by logistic regression and Cox regression, respectively. Our GRS was not consistently associated with any biochemical marker except for uric acid, arguing against pleiotropy. Uric acid was associated with a range of prevalent diseases, including coronary artery disease. Uric acid and the GRS were both associated with cardiovascular death and sudden cardiac death. In a multivariate model adjusted for factors including medication, causal HRs corresponding to each 1-mg/dl increase in genetically predicted uric acid concentration were significant for cardiovascular death (HR, 1.77; 95% confidence interval, 1.12 to 2.81) and sudden cardiac death (HR, 2.41; 95% confidence interval, 1.16 to 5.00). These results suggest that high uric acid is causally related to adverse cardiovascular outcomes, especially sudden cardiac death.

Hyperuricemia Is an Independent Predictor of Contrast-Induced Acute Kidney Injury and Mortality in Patients Undergoing Percutaneous Coronary Intervention

We investigated whether hyperuricemia is an independent predictor of contrast-induced acute kidney injury (CI-AKI) and mortality in patients undergoing percutaneous coronary intervention (PCI). In a single-center study of 1772 patients undergoing PCI, the development of CI-AKI and mortality during a 2.8-year median follow-up period was assessed. The incidence of CI-AKI was significantly higher in the hyperuricemic group than in the normouricemic group (5.78% vs 1.76%, P < .001). According to multivariate analysis (after adjusting for potential confounding factors), hyperuricemia predicted CI-AKI (odds ratio: 1.962; 95% confidence interval [CI]: 1.014-3.798; P = .045). The other risk factors for CI-AKI were >75 years, emergent PCI, chronic kidney disease (CKD), and anemia. Hyperuricemia with a tendency toward significantly independently predicted long-term mortality, after adjusting for CI-AKI, CKD, and emergent PCI (hazard ratio: 1.571; 95% CI: 1.006-2.452; P = .047). In patients undergoing PCI, hyperuricemia is associated with a risk of CI-AKI. Furthermore, after adjusting for other variables, including CI-AKI and CKD, long-term mortality after PCI was higher in those with hyperuricemia than with normouricemia.

Influence of urate-lowering therapies on renal handling of uric acid

The purpose of this study is to investigate the effect of urate-lowering therapies (ULTs) on renal uric acid excretion in gout patients. This prospective observational study involved 106 primary gout patients and 51 healthy controls. Gout patients received ULT with either xanthine oxidase inhibitors or the uricosuric agent benzbromarone. Parameters such as 24-h urinary uric acid, creatinine clearance, uric acid clearance, glomerular filtration load of uric acid, fractional excretion of uric acid, excretion of uric acid per volume of glomerular filtration, and urinary uric acid to urinary creatinine ratio were used to evaluate the pre- and post-treatment renal capacity for uric acid clearance in gout patients and were compared with the values in the healthy controls. Compared to healthy controls, gout patients had higher glomerular filtration load of uric acid and lower uric acid clearance, creatinine clearance, and fractional uric acid excretion. After ULT, both the xanthine oxidase inhibitor group and benzbromarone group patients showed reduction in glomerular filtration load of uric acid. Creatinine clearance was significantly improved in the xanthine oxidase inhibitor group. Excretion function was remarkably enhanced in patients who reached the treatment target (serum uric acid <6 mg/dl). Changes in glomerular uric acid filtration load were significantly correlated with changes in serum urate levels. Gout patients have impaired renal uric acid excretion. ULTs reduce renal urate load and enhance the renal capacity of uric acid clearance. Xanthine oxidase inhibitors showed superiority over benzbromarone in improving renal function.

Hyperuricemia and chronic kidney disease: an enigma yet to be solved

The role of uric acid (UA) on the pathogenesis and progression of chronic kidney disease (CKD) remains controversial. Experimental and clinical studies indicate that UA is associated with several risk factors of CKD including diabetes, hypertension, oxidative stress, and inflammation and hyperuricemia could be considered as a common dominator linking CKD and cardiovascular disease. Notably, the impact of serum UA levels on the survival of CKD, dialysis patients, and renal transplant recipients is also a matter of debate, as there are conflicting results from clinical studies. At present, there is no definite data whether UA is causal, compensatory, coincidental or it is only an epiphenomenon in these patients. In this article, we attempt to review and elucidate the dark side of this old molecule in CKD and renal transplantation.