Biochemical and clinical correlates of hypouricemia in surgical and critically ill patients

Background: Changes in plasma uric acid concentration (UA, mu mol/L) in postoperative and critical illness have pathophysiological and clinical relevance and may alter plasma antioxidant capacity. This issue is poorly understood because UA is simultaneously affected by multiple factors with impacts that have never been definitively characterized. Methods: Data from 1050 measurements of UA and additional variables obtained in 151 patients were processed using regression analysis. Results: The main direct correlate of UA was plasma creatinine (Cr), even in the absence of renal failure. UA was also related directly to sodium, glucose, cholesterol, albumin and other variables, and inversely to bilirubin. Postoperatively UA decreased, remaining related to preoperative UA and decreasing further with sepsis. In parenterally fed patients, UA was also inversely related to the amino acid dose. The following best fit explained three-quarters of its variability: UA=85.0(ln Cr, mu mol/L)+0.6(preoperative UA)+4.3 (sodium, mmol/L)+5.4(glucose, mmol/L)-0.2(bilirubin, mu mol/L)-28.9(amino acid dose, g/kg/day) - 935.6; n = 23 1, r(2) =0.74, p < 0.0001. A contribution of extremely low UA to impaired plasma antioxidant capacity was suggested in severe sepsis. Conclusions: These data show the combined effect of several factors on UA. The results may help to evaluate changes in UA in the clinical setting and pathophysiological events related to oxidative stress, and provide evidence of impaired plasma antioxidant capacity in severe sepsis.