P436 A study to compare detection of Aspergillus galactomannan in patients with clinically suspected invasive Aspergillosis using the Lateral Flow Assay (LFA) in comparison with Enzyme Linked Immunosorbent Assay (ELISA) and identification of new risk factors as per BM-AspICU criteria

POSTER SESSION 3, SEPTEMBER 23, 2022, 12:30 PM - 1:30 PM: OBJECTIVES: 1. To compare; 2. performance characteristics of lateral flow assay (Aspergillus galactomannan LFA, Immy, USA) in comparison with ELISA (Platelia™ Aspergillus antigen, Bio-Rad, France) for detection of galactomannan antigen in blood and BAL samples from suspected cases of Invasive Aspergillosis (IA); 3. turn-around time for reporting and the cost per test for both the methods: 1. To identify new host factors for categories of IA as per BM-AspICU (Hamam et al. Ann. Intensive Care, 2021) guidelines. METHODS: A total of 50 consecutive leftover samples (30 blood and 20 BAL) received for testing by Galactomannan assay by ELISA method were included. LFA and ELISA were performed as per manufacturers’ instructions. Results were recorded using the Digital Reader provided which gives readings as Positive ≥0.5 and <0.5 Negative. Additionally, results were read visually by two different people and graded as 0 (negative), 1+ (very faint band), 2+ (faint band), and 3+ (strong band). The values obtained by ELISA were reported as Galactomannan Index. Results of LFA and ELISA were compared. Patient profiles were studied to identify the possible and probable cases of IA as per BM-AspICU guidelines. RESULTS: Overall, 92% samples (n = 46) were positive with ELISA. Results of LFA and ELISA were comparable in 68% samples (n = 34). For all except two samples, visual readings of LFA (5 with 3+, 12 with 2 + and 19 with 1 + readings) correlated with digital readings. Sensitivity of LFA was 73.9% (95% CI). Applying BM-AspICU criteria, 28% (n = 14) were categorized as probable, 64% (n = 32) as possible cases of IA and 8% (n = 4) as NO IA. A total of 12 patients had classical host factors, 42% (n = 21) had other risk factors and we were able to identify 16% (n = 8) cases with new risk factors which were CNS involvement/brain injury/hemorrhage on mechanical ventilation. Clinical features were present in all of these 58% (n = 29) cases whereas radiological imaging was done in only 25 cases out of which 28% (n = 14) were positive. BM-AspICU criteria require ≥2 mycological criteria, but only two of the BAL samples were culture positive for Aspergillus species. These criteria could not be strictly applied to most patients in our study since invasive procedures such as BAL was not done, instead, blood was sent for galactomannan detection. The average turn-around time was 3-7 days for ELISA since the test was run twice a week whereas it was 5-24 h for the LFA. The pre-processing of samples and time required to perform the procedure for both the assays are similar. The cost per test for ELISA was Rs.1675/- as against LFA for Rs.750/-. CONCLUSION: LFA for galactomannan detection is an easier to perform, cost-effective method for diagnosis of IA as compared with ELISA. LFA overcomes the difficulty of insufficient volume of calibrators and controls provided with the ELISA kit. Useful especially for patients admitted in ICU where reports can be issued on the same day instead of batch testing. Identification of new risk factors and inclusion of the same under guidelines is essential to suspect and send samples for testing for early initiation of treatment.