Fractional excretion of urea as a guide to renal dysfunction.

The use of fractional excretion of sodium as a guide to renal perfusion is hampered by the prior use of natriuretic agents. The fractional excretion of urea (FEUr) has been shown to be affected by volume status. We, therefore, determined the value of the FEUr as a guide to renal perfusion. In 6 patients evaluated prospectively and in 87 patients evaluated retrospectively, a low FEUr (less than or equal to 35%) was found to be a sensitive index to renal perfusion, despite the prior administration of furosemide.