Magnesium hydrogen breath testusing end expiratory sampling toassessachlorhydria in

modified magnesiumhydrogen breath test, usingendexpiratory breathsam- pling, isdescribed toinvestigate achlor- hydria. Theefficacy ofthistestinthe diagnostic investigation of pernicious anaemia wascompared withthatofserum pepsinogen I.Twentyonepatients with pernicious anaemia- thatis,patients withachlorhydria - and22withhealed duodenal ulcerandnormalchlorhydria were studied. Magnesiumhydrogen breathtest, serumpepsinogen I,serum gastrin, andstandard gastric acidsecre- torytests wereperformed inallsubjects. Themean (SEM)hydrogen peakvalue was lowerinpatients withpernicious anaemia thanintheduodenal ulcer group (21-7 (1.9) v 71.3(5.2) ppm;p=0.00005). Thehydrogen peakvaluehada 95-2% sensitivity anda100%/o specificity todetect pentagastrin resistantachlorhydria.