单次甲烷呼气试验判断甲烷浓度高低的阈值选择:来自一个大型北美氢气-甲烷-二氧化碳呼气试验数据库的结果

Selection of a cut-off for high-and low-methane producers using a spot-methane breath test:results from a large north American dataset of hydrogen,methane and carbon dioxide measurements in breath

背景:甲烷-氢气呼气试验,是在加入碳水化合物底物后,每15-20 min间隔收集一次呼气标本,共10个样本,对这10个样本中甲烷和氢气浓度进行检测。采用该法判断氢气浓度的升高需要频繁的样本检测,而且氢气浓度升高otepad多发生于呼气试验后期;相较之下,甲烷浓度一般在底物加入前即可升高。如果将甲烷浓度作为呼气试验的主要目标,单次甲烷检测(例如收集禁食一晚后单个时间点的呼气样本,无需加入底物)或许足矣。方法:我们分析了11,674例连续检测的十样本乳酸呼气试验结果,这些病例来自于过去一年美国各州,所有呼气标本均在Commonwealth实验室(Salem,MA,USA)进行检测。将北美共识指南(NAC)的呼气试验标准作为参考标准。结果:参照NAC标准,该数据库病例的甲烷总体阳性率粗略为18.9%,校正后为20.4%。判断甲烷浓度高低的最佳阈值为≥4 ppm,其灵敏度为94.5%(可信区间:93.5%~95.4%),特异度为95.0%(可信区间:94.6%~95.5%)。采用校正因子(以5%的CO_(2)作为分子)进行校正后,有0.7%的高甲烷浓度重新判定为低浓度,2.1%的低甲烷浓度被判定为高浓度。结论:无论是基于本数据库所得出的≥4 ppm还是另一项单中心研究所描述的≥5 ppm作为呼气试验中甲烷基线浓度的阈值,用于判断传统十样本乳酸呼气试验检测小肠细菌过度生长时所诊断的“甲烷阳性”,都具有很高的准确性。

Background:Levels of breath methane,together with breath hydrogen,are determined by means of repeated collections of both,following ingestion of a carbohydrate substrate,at 15–20 minutes intervals,until 10 samples have been obtained.The frequent sampling is required to capture a rise of hydrogen emissions,which typically occur later in the test:in contrast,methane levels are typically elevated at baseline.If methane emissions represent the principal objective of the test,a spot methane test(i.e.a single-time-point sample taken after an overnight fast without administration of substrate)may be sufficient.Methods:We analysed 10-sample lactulose breath test data from 11674 consecutive unique subjects who submitted samples to Commonwealth Laboratories(Salem,MA,USA)from sites in all of the states of the USA over a one-year period.The North American Consensus(NAC)guidelines criteria for breath testing served as a reference standard.Results:The overall prevalence of methane-positive subjects(by NAC criteria)was 20.4%,based on corrected methane results,and 18.9% based on raw data.In our USA dataset,the optimal cut-off level to maximize sensitivity and specificity was4ppm CH4,94.5%[confidence interval(CI):93.5–95.4%]and 95.0%(CI:94.6–95.5%),respectively.The use of a correction factor(CF)(5%CO_(2) as numerator)led to reclassifications CH4-high to CH_(4)-low in 0.7% and CH_(4)-low to CH_(4)-high in 2.1%.Conclusions:A cut-off value for methane at baseline of either≥4 ppm,as in our USA dataset,or≥5 ppm,as described in a single institution study,are both highly accurate in identifying subjects at baseline that would be diagnosed as‘methanepositive’in a 10-sample lactulose breath test for small intestinal bacterial overgrowth.