Effects of prolonged, purine-free total parenteral and enteral nutrition on urate homeostasis in man

The influence on human urate homeostasis of prolonged, totally purine-free nutritional support, using total parenteral (TPN) or elemental enteral (EN) nutrition, is not well known. In a prospective study, we measured weekly serum uric acid, renal urate excretion and clearance, together with parameters of hydration, in 58 normally hydrated patients receiving prolonged (15 to 170 days) purine-free TPN (30 patients) or EN (28 patients) for various gastrointestinal disorders. A marked, early and sustained decrease (p less than 0.001) in serum uric acid was observed in TPN (155 +/- 9 mumol/l at day 7 versus 318 +/- 13 mumol/l before nutrition, mean +/- SEM) as well as in EN patients (192 +/- 11 mumol/l at day 7 versus 320 +/- 16 mumol/l before nutrition), together with a significant (p less than 0.01) rise in renal urate clearance. The urate clearance/glomerular filtration rate ratio increased significantly, while there was no significant change in natremia or plasma osmolarity. Serum urate and urate clearance returned to normal within 8 days of refeeding with a normally purine-containing diet. Replacement of TPN by EN or vice versa, or substitution of glucose by fructose resulted in no change in hypouricemia. A 4-day oral supply of purines (125 mg/day) in EN patients was associated with a 53% rise (p less than 0.01) in serum urate. We conclude that prolonged, purine-free TPN and elemental EN are a new cause of marked hypouricemia which is mainly due to increased urate clearance, the mechanism of the latter is still poorly known, but is not related to extracellular volume expansion.