Patients with parapneumonic effusions (PPE) measuring ,1 cm by lateral decubitus radiograph (LDR) or ,5 cm by lateral erect radiograph (LER) do not require thoracentesis. No such data exist for chest computed tomography (CCT). The objective of this study was to identify a PPE measurement by CCT that indicates the need for thoracentesis.A secondary data analysis of two pneumonia databases was conducted to identify patients with PPE. Measurements of PPE using LDR, LER and CCT were correlated by linear regression analysis. The clinical outcome of community-acquired pneumonia patients managed with the newly defined CCT measurement was evaluated.PPE was identified in 419 out of 1,460 patients with possible pneumonia. PPE measurements of 1 cm and 5 cm by LDR and LER, respectively, correlated with a measurement of 2.5 cm by CCT. Out of 95 patients with CCT measurements ,2.5 cm, 31 poor clinical outcomes were reported: outcome was PPE related (n51); outcome was PPE unrelated (n526); and outcome was not evaluable (n54). The single case of poor outcome also measured ,1 cm by LDR.This study indicates that patients with community-acquired pneumonia and a PPE measuring ,2.5 cm by CCT can be managed without the need for thoracentesis.

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