Serum uric acid (UA), the final product of purine degradation, has been shown to be increased in the hypoxic state. We assessed whether the presence of higher values of serum UA and serum UA to creatinine ratio is associated with clinical or functional characteristics in patients with chronic obstructive pulmonary disease (COPD). Fifty-nine consecutive stable patients with COPD, without comorbid conditions, were included. Clinical and functional characteristics were compared between patients with levels below and above the median values of serum UA and serum UA to creatinine ratio. Patients with serum UA levels above the median value differed significantly from the group with levels below this value only in FVC (p=0.04), and serum UA did not correlate significantly with the parameters analyzed. Patients with the serum UA to creatinine ratio above the median value had lower FVC (63 +/- 18 vs. 73 +/- 15 percentage of predicted, p=0.028), lower FEV(1) (43 +/- 19 vs. 55 +/- 18 percentage of predicted, p=0.019), and a higher level of dyspnea (MRC scale, 1.5 +/- 1.1 vs. 0.8 +/- 1.0, p=0.011). The serum UA to creatinine ratio correlated with FVC (r=-0.27), with FEV(1) (r=-0.31), and with dyspnea (r=0.29). In view of these results, we consider that the serum UA to creatinine ratio warrants evaluation as an additional parameter for predicting outcome in COPD.