False-positive results for ketone with the drug mesna and other free-sulfhydryl compounds.
All free-sulfhydryl compounds tested produced false-positive reactions in the Legal test for ketones. The color developed in the ketone pad of urine dipsticks [N-Multistix SG, Multistix 10 SG (Ames), and Chemstrip 9 (Boehringer-Mannheim)] was misinterpreted for ketone bodies, both by visual and automated reading. In contrast to the reaction with true ketones, a drop of glacial acetic acid added onto the ketone pad of dipsticks discharged the false-positive red color. A red-violet also developed instantly with free -SH compounds in the Acetest tablet assay (Ames), but quickly faded. In general, the presence of acidic groups such as -COOH and -SO3H in the structure appeared to increase the nitroprusside reactivity of free -SH compounds, whereas the presence of a -NH2 group appeared to decrease it. Currently, false-positive ketone reactions ascribable to a free -SH group are most likely to be seen for urine containing mesna. The false-positive test for ketones caused by free -SH compounds can be recognized and ruled out by proper procedures. On the other hand, this chromogenic reaction with free thiols might be used for monitoring urinary excretion of mesna.
D005189:False Positive Reactions; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007659:Ketones / Q000652:urine*; D007700:Kinetics; D008623:Mercaptoethanol / Q000031:analogs & derivatives*; D015122:Mercaptopurine / Q000627:therapeutic use; D015080:Mesna / Q000627:therapeutic use / Q000652:urine*; D009599:Nitroprusside; D011933:Reagent Kits, Diagnostic; D011934:Reagent Strips; D013438:Sulfhydryl Compounds / Q000652:urine*
D007659:Ketones; D011933:Reagent Kits, Diagnostic; D011934:Reagent Strips; D013438:Sulfhydryl Compounds; D009599:Nitroprusside; D008623:Mercaptoethanol; D015122:Mercaptopurine; D015080:Mesna