• Si Xuan, Kenneth M Zangwill, Weiyi Ni, Junjie Ma, and Joel W Hay.
• Leonard D. Schaeffer Center for Health Policy and Economics, University of Southern California, Los Angeles, CA, USA.
• J Gen Intern Med. 2020 Apr 1; 35 (4): 1102-1110.

BackgroundNo studies have evaluated the cost-effectiveness of single and two-step different diagnostic test strategies for Clostridioides difficile infection (CDI), including direct and indirect costs.ObjectiveTo evaluate the cost-effectiveness of commonly available diagnostic tests for CDI including nucleic acid amplification testing (NAAT) alone, glutamate dehydrogenase followed by enzyme immunoassay for toxin (GDH/EIA), GDH then NAAT (GDH/NAAT), and NAAT then EIA (NAAT/EIA).DesignDecision tree model from the US societal perspective with inputs derived from the literature. Willingness-to-pay threshold was set at $150,000 per quality-adjusted life year (QALY) gained. To assess the impact of uncertainty in model inputs on the findings, we performed one-way and probabilistic sensitivity analyses.ParticipantsWe conducted the analysis to represent a population aged 65 years old with diarrhea who received a CDI diagnostic test.Main MeasuresIncremental cost-effectiveness ratios (ICER) and incremental net monetary benefits (INMB).Key ResultsNAAT alone was the most cost-effective approach overall; GDH/NAAT was the most cost-effective two-step option. NAAT alone led to the highest QALYs gained, at an incremental cost of $54,547 (vs. GDH/NAAT), $55,410 (vs. GDH/EIA), and $50,231 (vs. NAAT/EIA) per QALY gained. NAAT/EIA was not cost-effective compared to any other strategy. GDH/NAAT resulted in a higher QALY compared to GDH/EIA, at an incremental cost of $96,841 per QALY gained. Variability in the likelihood of comorbidities, CDI probability, and age at disease onset did not substantially change the results. One-way sensitivity analyses showed that results were most sensitive to likelihood of recurrence, followed by CDI mortality rate and probability of severe CDI. Probabilistic sensitivity analyses explored known uncertainties in the base case and confirmed the robustness of the results.ConclusionsNAAT alone and GDH/NAAT (among the two-step options) were the most cost-effective diagnostic test approaches for CDI.

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