Serum 13C-bicarbonate in the assessment of gastric Helicobacter pylori urease activity.

Noninvasive detection of Helicobacter pylori (HP) requires serum or salivary antibody testing or the CO2 breath test. Since gastric HP produces a potent urease, a meal rich in 13C-labeled urea should lead to a measurable quantity of isotopic CO2 in the serum. This study investigates the feasibility, sensitivity, specificity, and potential of the measurement of serum 13C-bicarbonate (13CHCO3) in determining the presence of gastric HP. Nineteen patients with upper gastrointestinal symptoms assessed by intensity-duration questionnaire underwent endoscopy and biopsies for histology, Giemsa stain, and urease activity testing by CLOtest. Patients also consumed a 13C-urea-rich meal (5 mg/kg body weight, 99% 13C, MSD Isotopes, Montreal Canada). Serum was collected every 30 min for 3 h for quantitative determination of 13C by mass spectrometry. Fractional elevation of 13C after the enriched meal was then correlated with endoscopy, histology, and CLOtest. Fourteen of the 19 patients studied had histologic evidence of gastritis; 11 of 19 had positive CLOtest and had HP by histology and Giemsa stain. All HP-positive patients had significant elevation of 13CHCO3, compared with HP-negative patients. The mean maximum absolute change from baseline was 15.3 delta 13CHCO3 (range, 6.7-29.9) and occurred from 15 to 90 min; 13CHCO3 in HP-negative patients was significantly less (p < 0.05) than HP-positive patients with a mean value of 2.3 delta 13CHCO3 (range, 0-5.3). We conclude that serum 13CHCO3 analysis accurately reflects HP gastritis. This novel method is noninvasive, less labor intensive, less time consuming, and may have a value as a diagnostic screening tool for humans or in the assessment of the results of therapy in patients with HP infection.