Optimal fluid volume for detecting malignancy in serous effusions: a single institution experience

•Higher fluid volumes of serous fluids have higher rates of malignancy detection and low false-negative rate.•We recommend a minimum of 70 mL of serous fluid should be requested from clinicians for optimal cytopathologic examination.•Pericardial fluid is an exception, where optimal fluid volume will be much lower.•Our study will guide the cytopathology laboratory for requesting minimum serous fluid for rendering optimal diagnosis with confidence.