Lower serum uric acid level predicts mortality in dialysis patients

Abstract

We evaluated the impact of serum uric acid (SUA) on mortality in patients with chronic dialysis. A total of 4132 adult patients on dialysis were enrolled prospectively between August 2008 and September 2014. Among them, we included 1738 patients who maintained dialysis for at least 3 months and had available SUA in the database. We categorized the time averaged-SUA (TA-SUA) into 5 groups: <5.5, 5.5-6.4, 6.5-7.4, 7.5-8.4, and ≥8.5 mg/dL. Cox regression analysis was used to calculate the hazard ratio (HR) of all-cause mortality according to SUA group. The mean TA-SUA level was slightly higher in men than in women. Patients with lower TA-SUA level tended to have lower body mass index (BMI), phosphorus, serum albumin level, higher proportion of diabetes mellitus (DM), and higher proportion of malnourishment on the subjective global assessment (SGA). During a median follow-up of 43.9 months, 206 patients died. Patients with the highest SUA had a similar risk to the middle 3 TA-SUA groups, but the lowest TA-SUA group had a significantly elevated HR for mortality. The lowest TA-SUA group was significantly associated with increased all-cause mortality (adjusted HR, 1.720; 95% confidence interval, 1.007-2.937; P = 0.047) even after adjusting for demographic, comorbid, nutritional covariables, and medication use that could affect SUA levels. This association was prominent in patients with well nourishment on the SGA, a preserved serum albumin level, a higher BMI, and concomitant DM although these parameters had no significant interaction in the TA-SUA-mortality relationship except DM. In conclusion, a lower TA-SUA level <5.5 mg/dL predicted all-cause mortality in patients with chronic dialysis.

Figure 1.

Flow chart of study enrollment. Between August 2008 and September 2014, a total of 1739 prevalent dialysis patients were included.

Figure 2.

Distribution of the time-averaged serum uric acid levels according to sex. Most of the time-averaged serum uric acid levels in men (white empty bar) overlap with those in women (gray-filled bar), although they are slightly deviated to the right side.

Figure 3.

Mortality rates and hazard ratios according to the time-averaged serum uric acid level. This graph shows the crude mortality rate according to the TA-SUA groups. The lowest TA-SUA group has a significantly increased mortality rate compared with the other 4 TA-SUA groups. The log hazard ratios for mortality in relation to the TA-SUA level are presented. A U-shape relationship is plotted between mortality and the TA-SUA level in patients with end-stage renal disease.

Figure 4.

Kaplan–Meier curve according to the time-averaged serum uric acid level above and below 5.5 mg/dL. A, Patients with the TA-SUA <5.5 mg/dL had a higher mortality rate compared with those with TA-SUA ≥5.5 mg/dL. B, A similar trend was observed when divided into HD and PD groups. TA-SUA = time-averaged serum uric acid.

Figure 5.

Stratification analyses. A comparison of the adjusted hazard ratios for the subgroups is presented by forest plot. ^a Adjusted for age, sex, the dialysis type, body mass index, systolic blood pressure, calcium level, phosphorus level, albumin level, total cholesterol level, uric acid level, subjective global assessment, and DM for each subgroup (excluding its own group).