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

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Abstract
Methocarbamol, a widely prescribed muscle relaxant, gives a positive result for increased vanilmandelic acid excretion with the useful screening test devised by Gitlow for evidence of pheochromocytoma. Evidence for the presence of this drug can be obtained from a positive color reaction with the 5-hydroxyindoleacetic acid test, used in the screening for carcinoid tumor.