Measurement Of Exhaled Ammonia By Ion Mobility Spectrometry In The Diagnosis Of Helicobacter Pylori Infection

Background:Helicobacter pylori（H.pylori）infection is the major causative factor of chronic gastritis,peptic ulcer,mucosa-associated lymphoid tissue（MALT）lymphoma and gastric cancer.H.pylori can produce highly active urease,which can enzymically catalyzes the hydrolysis of urea to CO₂ and ammonia,and the primary method for H.pylori diagnosis is carbon-13 urea breath test（UBT）.Due to lack of manufacturing capacity of carbon-13 isotope labeling,high cost,the accessibility of UBT is limited.At the same time,H.pylori can also produce ammonia when it decomposes urea.The measurement of exhaled ammonia with unlabeled common urea can be used to detect H.pylori infection.Ion mobility spectrometry（IMS）is a gas phase separation technique for the sensitive and selective identification and quantification of trace substances,which has the advantages of fast,sensitive,simple structure,and portability,and is very suitable for online measurement of exhaled ammonia in real time.Objective:To develop an online measurement method for exhaled ammonia that meets the requirements of clinical application with high sensitivity and specificity,and to explore the relationship between the concentration of exhaled ammonia with urea intaking and H.pylori infection.Finally,to evaluate the application value of exhaled ammonia in the diagnosis of H.pylori infection.Method:Firstly,high selectivity and specificity measurement of ammonia was achieved by positive photoionization with acetone reagent as a modifier.The online dilution and purging sampling method was used to reduce the effects of high humidity and ammonia adsorption on the measurement of exhaled ammonia.In addition,performance parameters include quantitative linear range and limit of detection were evaluated,and detection of actual exhaled breath samples were performed.Subsequently,exhaled ammonia was measured from July to November 2022 in 318people undergoing UBT at the Health Management Center of Dalian Medical University Second Affiliated Hospital.The difference of ammonia concentration in exhaled breath between H.pylori infected and uninfected persons was analyzed,and the value of exhaled ammonia in diagnosis of Hp infection was evaluated by receiver operating characteristic curve（ROC）.Results:1.Acetone-modifier positive ion photoionization IMS has a high specificity for the measurement of exhaled ammonia.With acetone as a modifier,the good peak-to-peak resolution between the reagent ion peak and the product ion peak,thus improving the qualitative detection of ammonia in exhaled breath.2.The online dilution gas reduced the effect of humidity,and the online purging gas reduced the effect of ammonia adsorption,having achieved the measurement of exhaled ammonia in real time.3.The quantitative curves for the high and low concentration range were obtained to meet the requirements for the detection range of human exhaled ammonia concentration.4.The concentration of oral exhaled ammonia was compared with that of nasal exhaled ammonia.The concentration of oral exhaled ammonia was significantly affected by the mouth cavity origin of ammonia.5.A total of 318 subjects were included in the study.According to the carbon-14 UBT results,101 of them were H.pylori-positive and 217 were negative.6.There was no significant difference in baseline exhaled ammonia concentration（C1）between the H.pylori positive group and the negative group（49.4±19.3 ppb vs 57.5±20.9 ppb,P=0.181）.The exhaled ammonia concentration difference（C2-C1）of the H.pylori positive group in pre-and post-urea intake was significantly higher than that of the negative group（21.7±16.0ppb vs 0.2±13.7 ppb,P<0.001）.The exhaled ammonia concentration change rate（CCR,%）of the H.pylori positive group in pre-and post-urea intake was significantly higher than that of the negative group（47.5±39.3%vs 1.6±17.9%,P<0.001）.7.The ROC analysis results indicated that the C2-C1 and CCR are significant for the diagnosis of H.pylori infection.With 14C-UBT results as the diagnosis gold standard,the area under the ROC curve（AUC）of C2-C1 was 0.904.With cutoff value of 9.3ppb,the sensitivity was 84.2%and the specificity was 90.8%,whereas the positive predictive value（PPV）was 81.0%（85/105 cases）,the negative predictive value（NPV）was 92.5%（197/213 cases）,and the overall predictive accuracy was 88.7%（282/318cases）.The area under the ROC curve（AUC）of CCR was 0.919.With cutoff value of20.2%,the sensitivity was 84.2%and the specificity was 92.2%,whereas the positive predictive value（PPV）was 83.3%（85/102 cases）,the negative predictive value（NPV）was 92.6%（200/216 cases）,and the overall predictive accuracy was 89.6%（285/318cases）.The diagnostic value of the CCR is slightly better than the C2-C1.Conclusion:IMS is a reliable method for detecting ammonia in human exhaled breath with high specificity and sensitivity.The results of this exploratory study indicated that the measurement of exhaled ammonia is significant for the diagnosis of H.pylori infection and provides a valuable new method for the diagnosis of H.pylori infection.