High uric acid and urea clearance in cirrhosis secondary to increased "effective vascular volume"

Since urea and uric acid clearance are affected by the effective intravascular volume, we measured the fractional urea and uric acid excretion in cirrhosis. High urea and uric acid clearances were observed in 30 and 55 percent, respectively, of 20 consecutive cirrhotic patients with normal renal function. In seven patients with a high fractional uric acid excretion, 5 mg of isosorbide dinitrate every four hours for 24 hours induced a significant increase in the serum uric acid level (from 3.7 +/- 0.8 mg/dl to 4.4 +/- 0.8 mg/dl; less than 0.001) with a concomitant decrease in the fractional uric acid excretion (from 14.0 +/- 3.2 percent to 8.8 +/- 3.1 percent; less than 0.02). During the same test, the blood urea level increased from 3.3 +/- 1.1 mmol/liter to 4.1 +/- 1.2 mmol/liter (p less than 0.005) with a decrease in fractional excretion from 51 +/- 4.5 percent to 39 +/- 5 percent (p less than 0.001). The oral intake of sulfinpyrazone in six of these patients induced a normal uricosuric response. In two cirrhotic patients with ascites, 40 mg of furosemide associated with a 24-hour severe water restriction was also shown to normalize the high fractional excretion of both urea and uric acid. In nine patients with ascites, we observed a significant increase in blood urea and uric acid concentration despite the absence of change in creatinine clearance once ascites was removed by diuretics. On the basis of these findings, we believe that the high fractional excretion of both urea and uric acid frequently observed in cirrhosis is related to an increase in the effective vascular volume.