Effect of furosemide on urinary excretion of 4-hydroxy-3-methoxymandelic acid (VMA).

Excretion of VMA was measured in 10 healthy volunteers before and after intake of 40 mg furosemide and in 3 patients with congestive heart failure who were intermittently treated with 80 mg furosemide. In healthy volunteers furosemide caused an increase in VMA excretion from 5.0 +/- 0.5 to 7.8 +/- 0.9 mg/24 h and from 2.0 +/- 0.2 to 2.9 +/- 0.3 mg/g creatinine (mean +/- SE). Excretion of catecholamines was slightly increased in some subjects, but did not reach the upper limit of normal in any case. Furosemide induced an acute increase in urinary VMA that could have derived from inhibition of renal tubular reabsorption. Administration of furosemide might result, on occasion, in a false positive test for pheochromocytoma.