Storage of pleural fluid may be crucial for cytological analysis

<bold>Background:</bold> Pleural effusion (PE) is a common condition with multiple causes, of which management starts from pleural thoracocentesis (PT). Many institutions, especially district hospitals, do not have on-site analysis of pleural fluid (PF) due to lack of laboratory and need to refer PT samples. However, the consequences of the delay of the analysis and storage of PF samples on the cytological diagnosis are unknown. <bold>Objective:</bold> To determine the effect of time and storage on cytological analysis of PF. Materials and methods: We included 31 consecutive patients presented with pleural effusion during a 6 month-period. After PT, the pleural fluid collected was divided into 6 samples and stored using two methods: ambient air and storage at 4°C, then processed in pairs at hour 0 (h0), h24 and h72 before a blind cytological analysis. The identification of tumor cells and quality of all samples were evaluated. <bold>Results:</bold> Malignant cells were identified in 11 patients (35.5%). There was a significant alteration of tumor cells over time in ambient air (p=0.029) which was not the case in storage at 4°C (p=0.49). There was a significant alteration in the quality of pleural fluid cells analysis over time, in both ambient air (p<0.0001) and storage at 4°C (p<0.0001). <bold>Conclusion:</bold> Our study showed that a delay from PT to cytological analysis and ambient air storage of the sample may affect negatively pleural fluid cytological analysis. Therefore, we suggest immediate analysis or sample storage at 4°C before referring the sample.