Novel T2 Magnetic Resonance Assay Compared to Standard Blood Cultures for Detection of Candidemia.

Abstract

Background. Outcomes of candidemia are improved with rapid diagnosis and therapy. Blood culture (BC) has a turn-around-time (TAT) of 2-5 days. T2 magnetic resonance (T2) assay, a nano-diagnostic blood test, detects: C. albicans/C. tropicalis (Ca/Ct), C. krusei/C. glabrata (Ck/Cg), and C. parapsilosis (Cp). Clinical trials of T2 showed good sensitivity and specificity, NPV 99% and TAT of 3-5 hours. We evaluated use and performance characteristics of T2 assay at our institution. Methods. Observational, retrospective, cross-sectional evaluation of patients with suspected candidemia who had T2 performed from October 2015 to April 2016 at Henry Ford Health System, a large healthcare system in Detroit, MI. Candida Score of >3was defined as high risk for candidemia. Discordant results of T2 and BC were assessed. PPV and NPV were calculated for all specimens versus specimens drawn simultaneously. Results. Of 120 patients, 33 (28%) had positive T2 and/or BC. Ten of 33 (30%) had T2 and BC positive and 23/33 (70%) were discordant. Possible reasons for discordance: different dates of blood collection (30%); antifungal therapy before collection (35%); Candida sp. not detected by T2 (4%). Eleven of 33 (33%) had only positive BC: 5 Cg, 3 Ca, 2 Cp, 1 C. lusitaniae. The average Candida score 2.1 (0-4), other characteristics in the table. Twelve of33 (37%) had only positive T2: 7 Ca/Ct, 3 Cp, 2 Cg/Ck. The average Candida score was 2.1 (0-5). The average TAT for T2 was 13 hours (5-41) and 34 hours (21-109) to initial positive BC and 4 days (3-13) to final positive BC. The overall PPV and NPV for T2 were 45% and 89% versus 60% and 95% for simultaneous specimens. Conclusion. Performance characteristics of T2 in routine clinical practice differ from those reported in clinical trials. Targeted use of T2 in only high-risk patients and uniformity in sample collection will be important for accurate interpretation of this test. The rapid TAT and good NPV of T2 should help support antimicrobial stewardship efforts.