Serum uric acid, creatinine, and the assessment of antioxidant capacity in critical illness

Abstract

In their nice study on serum total antioxidant capacity (TAC) in sepsis [1] Chuang and coworkers have demonstrated an increase in TAC that was directly correlated to severity of illness and poor outcome, and to increasing levels of serum uric acid (UA). Although the increase in TAC might be interpreted as an extreme protective attempt against overwhelming inflammation, this must still be proved, as correctly commented on by the authors. A critical point is that, although increasing UA enhances TAC, the pathophysiological relevance depends on the underlying mechanism, which may include detrimental factors, such as renal dysfunction. In this case the obvious concern is the organ dysfunction causing UA to increase, while the consequent increase in TAC should be considered coincidental. To ease this interpretation one should at least examine the relationship between UA or TAC and plasma creatinine concentration (assuming that creatinine always accurately reflects renal function). Simply excluding patients with plasma creatinine >3.0 mg/dl or on hemodialysis [1] may not be sufficient to rule out an impact of moderate changes in renal function on UA. We are mentioning this because, in an on-going study on changes in UA on more than 100 surgical patients with moderate to extreme illness, we found that 34% of the variability of UA was still controlled by creatinine concentration, even when excluding cases with creatinine >1.8: UA = 0.5 + 3.4(creatinine); r = 0.58, r2 = 0.34, p < 0.001, n = 1,005 (means ± SD, ranges: UA = 3.6 ± 1.6 mg/dl, 0.2 to 9.2; creatinine = 0.9 ± 0.3 mg/dl, 0.3 to 1.8). Within this regression, septic patients showed a tendency for lower UA for any creatinine level, compared to nonseptics (p < 0.001). Constructively, it would be interesting to know details of the relationship between UA or TAC and creatinine in the patients studied by Chuang and colleagues [1]. This might help to assess the impact of even moderate changes in renal function on TAC, or it may be an idea for future investigations. We would like to congratulate the authors once more for their nice study.