642. Higher Diagnostic Accuracy with Ultrasensitive Detection of Helicobacter pylori Stool Antigen Using Single-Molecule Counting Technology

BACKGROUND: Current diagnostic methods for Helicobacter pylori infection include fecal antigen tests, (13)C-urea breath test, and gastric biopsy. The breath test is limited by poor specificity and the fecal antigen tests by poor sensitivity. We have developed a prototype assay for detection of H. pylori antigen in human stool, powered by ultrasensitive Single Molecule Counting technology, and compared the analytical performance to a commercially available enzyme-linked immunoassay (EIA) antigen test. METHODS: The Singulex Clarity H. pylori antigen assay incubates diluted stool with capture and fluorescent-labeled detection antibodies. After incubation and wash steps, fluorescent molecules are eluted and single-molecule fluorescence measured by detected events (DE′). Analytical performance was compared with a commercial EIA (Premier Platinum HpSA(®) Plus, Meridian Bioscience, Inc.) using serial dilutions of H. pylori control (~37,500–1.7 ng/mL) and high positive stool (signal to noise ratio >2). Clinical performance was evaluated using two cohorts, one had 10 EIA-negative and 10 EIA-positive samples and the other 13 high positives (> 0.500 at 450/630) and 5 low positives near the EIA cutoff (0.100–0.500 at 450/630). One sample was excluded due to discordant EIA results, and three to reader flags. RESULTS: The lower limit of detection of the Clarity H. pylori assay was 1.7 ng/mL and the EIA 1,250 ng/mL (IFU: LOD 4.67 ng/mL). A high positive stool sample was detectable by the Clarity H. pylori assay diluted 1:10,000,000 and by the EIA 1:10,000. The Clarity H. pylori assay showed a 729-fold increase in lower limit of detection and 1,000-fold increase in endogenous antigen lower limit of detection compared with the EIA. Clarity signal ranged from 46–665 DE’ for EIA-negative samples and 487,484–576,747 DE’ for EIA-positive samples. CONCLUSION: The Singulex Clarity H. pylori antigen assay may have orders of magnitude higher analytical sensitivity than the commercial EIA and demonstrated 100% positive agreement and 100% negative agreement on detection of H. pylori antigen in human stool samples. The ultrasensitive Clarity H. pylori assay has the potential for high sensitivity and specificity to improve current diagnostic options for H. pylori infection; however, additional multicenter studies are required. DISCLOSURES: All authors: No reported disclosures.