False Positive Reaction Due to Methocarbamol in the Screening Test for Vanilmandelic Acid (vma).

I N PHEOCHROMOCYTOMA, 3-methoxy-4-hydroxy-rnandelic acid (VMA), a metabolite of epinephrine and norepinephrine, is excreted in urine in abnormally large quantities. Qitlow et al. (1) have developed a semi quantitative screening method for VMA that we have found to be useful and reliable. The procedure is particularly welcome because it permits screening of a large number of urines from hypertensive patients and is much more convenient than the measurement of catecholamines. Also, a reagent kit based on Gitlow’s colorimetric reaction is commercially available.* We have performed more than 400 such urine tests and 2 patients in whom the tests indicated increased YMA were surgically proved to have pheochromocytomas. Briefly, the test as described by Gitlow involves extraction of the acidified urine with ethyl acetate, evaporation of the solvent, and solution of the residue in dilute K2C03. Diazotized p-nitroaniline is added and the mauve-colored azo-VMA product is extracted into amyl alcohol made alkaline with ethanolamine. Two readings are made in a