Interference by formaldehydogenic drugs in the quantitative determination of urinary hydroxyindoleacetic acid.

The administration of methenamine mandelate (Mandelamine) to normal individuals and patients with carcinoid resulted in a marked reductionin apparent urinary hydroxyindoleaceticacid (HIAA) as determined by the quantitative nitroso-naphthol method. Mandelamine, methenamine, and formaldehyde inhibited the normal color development in vitro. The interfering reaction is dependent on an acid pH and is not reversed by raising the pH. It is suggestedthat formaldehyde is the active substance and the role of mandelamine and methenamine is that of a precursor of this substance in acidsolution. Chloride and sulfate ions, per se, caused a definite but limited interference with the color reaction. Under the conditions of this study, mandelamine did not prevent detection of elevated urinary HIAA by the qualitative test for HIAA.