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Background Pleural fluid is routinely sent for cytological and microbiological analysis during local anaesthetic thoracoscopy (LAT) in patients with unexplained unilateral pleural effusion. However, there is currently no established guidance on the utility of additional fluid analysis alongside pleural biopsy.Aim To evaluate the diagnostic utility and cost effectiveness of concurrent pleural fluid cytological and microbiological analysis during LAT, in addition to pleural biopsy for histology and microbiology.Method Retrospective analysis of 123 consecutive LAT procedures performed between January 2022 and December 2024. Cytological analysis was performed on 93 pleural fluid samples and results were categorised as: no malignant cells, atypical cells, malignant cells with insufficient sample for molecular markers, or malignant cells with sufficient sample. Microbiological analysis, including bacterial and mycobacterial cultures, was performed on 109 samples and categorised as: clinically relevant growth or no growth.Results Of the 123 patients, mean age was 74.2 years and male 78% (96).Of the 93 fluid cytology samples: 58 (62%) showed no malignant cells, of these 22 had malignancy confirmed on pleural biopsy, 32 showed fibrous pleuritis, and 4 were unremarkable. 8 (7%) showed atypical cells, of which 7 had confirmed malignancy on pleural biopsy and 1 was benign. 12 (13%) cytology samples showed malignant cells insufficient for molecular markers, and all had confirmed pleural malignancy on biopsies. 15 (16%) demonstrated malignant cells sufficient for molecular markers and all had confirmed pleural malignancy on biopsies.Of 109 pleural fluid samples sent for bacterial and mycobacterial cultures: 2 grew organisms of no clinical significance, and 1 showed contaminant growth. One patient had positive pleural biopsy culture for acid fast bacilli, with negative pleural fluid culture.Pleural fluid cytological, bacterial and mycobacterial analyses incurred an additional cost of £37, £27 pounds and £50 per patient, respectively.Abstract P274 Table 1Conclusion Cytological analysis of pleural fluid during LAT did not provide additional diagnostic value or alter patient management. Similarly, microbiological cultures showed no growth, in the absence of clinical suspicion of infection. Routine use of these tests add healthcare costs without any benefit. Microbiological analysis, however, could be considered in clinically relevant cases where infection is suspected.