The prognostic impact of the uric acid level in patients who require cardiovascular intensive care - is serum uric acid a surrogate biomarker for critical patients in the non-surgical intensive care unit?

Background: The prognostic impact of hyperuricemia and the factors that induce hyperuricemia in cardiovascular intensive care patients remain unclear. Methods and results: A total of 3257 emergency department patients were screened, and data for 2435 patients who were admitted to an intensive care unit were analyzed. The serum uric acid level was measured within 15 min of admission. The patients were assigned to a low-uric acid group (uric acid <= 7.0 mg/dl, n=1595) or a high-uric acid group (uric acid >7.0 mg/dl, n=840) according to their uric acid level on admission. Thereafter, the patients were divided into four groups according to the quartiles of their serum uric acid level (Q1, Q2, Q3 and Q4), and uric acid levels and Acute Physiology and Chronic Health Evaluation II (APACHE II) score. A Kaplan-Meier curve showed a significantly lower 365-day survival rate in a high-uric acid group than in a low-uric acid group, and in Q3 than in Q1 or Q2 and in Q4 than in the other groups. The multivariate logistic regression model for 30-day mortality identified Q4 (odds ratio: 1.856, 95% confidence interval (CI) 1.140-3.022; p=0.013) as an independent predictor of 30-day mortality. The area under the receiver-operating characteristic curve values of the serum uric acid level and APACHE II score for the prediction of 30-day mortality were 0.648 and 0.800, respectively. The category-free net reclassification improvement and integrated discrimination improvement showed that the calculated risk shifted to the correct direction by adding the serum uric acid level to the APACHE II score (0.204, 95% CI 0.065-0.344; p=0.004, and 0.015, 95% CI 0.005-0.025; p=0.004, respectively). The prognosis, including the 365-day mortality, among patients with a high uric acid level and a high APACHE II score was significantly poorer in comparison with other patients. Conclusion: The serum uric acid level, which might be elevated by the various critical stimuli on admission, was an independent predictor in patients who were emergently hospitalized in the intensive care unit. The serum uric acid level is therefore useful as a surrogate biomarker for critical patients in the intensive care unit.