Serum urate is associated with baseline renal dysfunction but not survival or deterioration in renal function in malignant phase hypertension.

Abstract

There has been speculation whether serum uric acid levels are an independent prognostic factor in patients with hypertension. To investigate the clinical associations and prognostic value of serum urate in patients with malignant phase hypertension (MHT), by comparing clinical features in patients with serum urate levels above and below the median levels for this population, and secondly, by performing a survival analysis in these patients. Review of the data on 153 patients (98 males; mean age 50.3 years, SD 13.5) with MHT on the west Birmingham MHT register. Median uric acid levels in this population was 0.41 mmol/l (6.9 mg/dl), with an interquartile range of 0.34-0.50 mmol/l (5.7-8.4 mg/dl). Clinical characteristics of patients with a serum urate <0.41mmol/1 (group 1) were compared to those with levels above the median (0.41 mmol/l, group 2). Mean duration of follow-up was similar in both groups. The mean diastolic blood pressure at presentation and both mean systolic and diastolic blood pressures at follow-up were significantly higher in group 2 (that is, those with high serum urate levels) (unpaired t test, P= 0.039). There was also more renal dysfunction in group 2 patients with MHT, with higher mean serum urea and creatinine levels, both at presentation and at follow-up (unpaired t test, P< 0.01). The commonest causes of death were myocardial infarction (n = 7), heart failure (n = 4), stroke (n = 10) and renal failure (n = 5). There was no difference in mean survival duration between groups 1 and 2 (Kaplan-Meier, 64.6 versus 66.8 months; log-rank test, P= 0.519). Serum urate levels also did not predict the rise in serum creatinine levels (log-rank test, P= 0.84) or urea (P= 0.4033) amongst these patients. Using a multivariate Cox proportional hazards analysis, the only independent predictors of outcomes (death or the need for dialysis) were age (P = 0.007) and serum creatinine levels at presentation (P = 0.0046). Our analysis of a large series of patients with MHT shows that those with high urate levels had higher diastolic blood pressures and greater renal impairment at baseline. At follow-up, patients with median serum urate >0.41 mmol/l showed a greater deterioration in renal function and higher blood pressures, but no significant difference in survival. Serum urate levels also do not appear to be predictive of the deterioration in renal function or overall survival in patients with MHT.