1713. Impact of False-Positive Low-Titer Cryptococcal Antigen Testing

BACKGROUND: At University of Kentucky (UK) HealthCare, the transition from latex agglutination testing (Remel, Lenexa, KS) to IMMY Cryptococcal Antigen Lateral Flow Assay (CrAg LFA) occurred in September 2016. A few months later, it was noticed that several cryptococcal cases were diagnosed with weak positive test results where the diagnosis could not be confirmed by additional testing. The purpose of this study was to analyze the characteristics of these patients, and to assess the interventions they received based on positive results. METHODS: This was a retrospective study of the patients with positive CrAg LFA treated at UK HealthCare from November to December 2016. Low antigen titers (≤ 1:20) were considered to be false positive if repeat testing with the Remel Cryptococcal Latex assay, IMMY latex and IMMY microwell EIA were negative, cultures and histopathology were negative and there was no clear clinical evidence of infection. RESULTS: During this 2-month period, CrAg LFA was positive in 12 patients. The diagnosis of cryptococcosis could not be confirmed by additional testing in 9 (75%) individuals. Cirrhosis/liver disease was present in 3 (33.3%) patients, 5 (55.6%) underwent lumber puncture and antifungal therapy was administered in 8 (88.9%) patients (Table 1). CrAg LFA was false positive in 1/2 (50%) HIV, 3/3 (100%) transplant, and 5/7 (71.4%) non-HIV/non-transplant patients (Figure 1). Among the false positives, 4 (44.4%) patients had titer of 1:5, two (22.2%) had 1:20, and the original positive screen was not detected upon titration in 3 (33.3%) other patients. One HIV patient received a complete treatment course for unconfirmed cryptococcal meningitis because an LP could not be performed. CONCLUSION: False-positive low CrAg LFA titers led to unnecessary tests, antifungal treatments and prolonged hospitalization in some patients. One-third of these individuals had cirrhosis/liver disease. Other institutions also reported false-positive low CrAg LFA titers. As a result, the company staged a recall of the specific lot and corrected the problem in reagent manufacturing. Low-positive titers using CrAg LFA should be interpreted carefully and further testing should be considered as determined by the clinical situation. [Image: see text] [Image: see text] DISCLOSURES: All authors: No reported disclosures.