Poster (15W219)

Does the use of Lidocaine spray during upper GI endoscopy result in false positive CLO test?


Gumani D, Shah R, Muthalagu P


Cavan and Monaghan Group of Hospitals


Testing for Helicobacter Pylori is a standard protocol during endoscopic procedures. The question is whether we are treating a genuine Helicobacter Pylori infection, or are we treating a false positive CLO test with unnecessary antibiotics?


CLO test (Campylobacter-like organism test), is a rapid diagnostic test for Helicobacter pylori infection. A biopsy from the gastric mucosa is placed into a medium containing urea and an indicator such as phenol red. The urease produced by H. pylori hydrolyses urea to ammonia, which raises the pH of the medium, and changes the colour of the specimen from yellow (NEGATIVE) to red (POSITIVE).Lidocaine spray is usually applied topically on the throat before an upper digestive endoscopy procedure. It contains sodium hydroxide and/or hydrochloric acid for pH adjustment (pH 6.5). Sodium hydroxide reacts with urea to produce sodium cyanate, ammonia and water. Therefore, as witnessed, if lidocaine is sprayed directly on a CLO well, the result will be a red specimen giving a false positive result. Hence, this study is designed to demonstrate if Lidocaine is indeed influencing the CLO result.


A prospective study conducted between the period of May to June 2015 with an estimate of 200 patients undergoing endoscopic procedures for investigation of upper GI pathologies and follow up. Our study was approved by the HSE Ethics Committee in Kells, focuses on finding and eliminating the factors that may give a false positive CLO test. Lidocaine spray was used before each procedure. Biopsies and aspirates were taken from the gastric mucosa for the CLO test as well as for histology examination to compare the results.


The study was predictably closed earlier as 44 of 50 patients showed no positive CLO test on gastric aspirate and 46 of 50 patients had negative CLO tests on antral biopsy however, 7 had positive H.Pylori on histology with 4 lidocaine sprays. Subsequently, when 8 sprays were administered for 10 random patients, 7 had positive CLO (aspirate) test, 3 had positive CLO (antral biopsy) test whilst, none of them had positive histology.


Our study demonstrates that Lidocaine spray used in appropriate doses does not influence CLO test results. However, overuse of the spray may mislead the test result, since the reaction of Lidocaine spray and urea from the CLO test produces ammonia as does Helicobacter Pylori when it reacts with urea, hence giving the positive red result for a rapid urease test.