title: Methylene blue in the evaluation of gastrointestinal tract integrity: potential limitations.
abstract: BACKGROUND
  The integrity of the gastrointestinal tract can be evaluated by oral or rectal application of methylene blue. In the presence of anastomotic leaks or fistulas, methylene blue can be recovered in adjacent drains. However, parts of the dye can biochemically be reduced by intestinal bacteria to its colorless form leucomethylene blue, limiting the prediction of the test.
  
  
  METHODS
  Diluted methylene blue was added to different concentrations of bacterial suspensions of Escherichia coli and Enterococcus faecalis. The time for discoloration of the suspension was measured.
  
  
  RESULTS
  Reduction of methylene blue to leucomethylene blue was observed in both types of bacterial suspension. A 10(8) bacterial concentration discolorated the dye within 1 h in the E. faecalis suspension, respectively 2.5 h in the E. coli suspension. Longer bacterial interaction with methylene blue reduced the bacterial concentration required to achieve complete discoloration.
  
  
  CONCLUSIONS
  Methylene blue can reliably be used as routine diagnostic test for the assessment of upper gastrointestinal integrity, where bacterial load is low. In the lower gastrointestinal tract, where bacterial load is generally higher, the dye can indicate leaks, only if extended intestinal passage after oral ingestion is avoided. In all other cases, the examiner has to be aware of false-negative results by bacterial discoloration of methylene blue.
authors.affiliation: Department of Surgery, University Hospital Mannheim, Ruprecht Karls University Heidelberg, Mannheim, Germany. ruediger@prosst.de
authors.forename: R L
authors.initials: RL
authors.lastname: Prosst
authors.forename: Franziska
authors.initials: F
authors.lastname: Reinecke
authors.forename: G
authors.initials: G
authors.lastname: Geginat
mesh_terms: D000818:Animals; D013293:Enterococcus faecalis / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D041981:Gastrointestinal Tract / Q000033:anatomy & histology* / Q000378:metabolism; D006801:Humans; D008751:Methylene Blue / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D013194:Staining and Labeling / Q000379:methods*
chemical_list: C011010:hydromethylthionine; D008751:Methylene Blue