False-positive results for ketone with the drug mesna and other free-sulfhydryl compounds

Clin Chem. 1987 Feb;33(2 Pt 1):289-92.


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.

MeSH terms

  • False Positive Reactions
  • Humans
  • Hydrogen-Ion Concentration
  • Ketones / urine*
  • Kinetics
  • Mercaptoethanol / analogs & derivatives*
  • Mercaptopurine / therapeutic use
  • Mesna / therapeutic use
  • Mesna / urine*
  • Nitroprusside
  • Reagent Kits, Diagnostic
  • Reagent Strips
  • Sulfhydryl Compounds / urine*


  • Ketones
  • Reagent Kits, Diagnostic
  • Reagent Strips
  • Sulfhydryl Compounds
  • Nitroprusside
  • Mercaptoethanol
  • Mercaptopurine
  • Mesna