Observations of pleural fluid helpful in diagnosis

	Suggested diagnosis
Color of fluid
Pale yellow (straw)	Transudate, some exudates
Red (bloody)	Malignancy, benign asbestos pleural effusion, postcardiac injury syndrome, or pulmonary infarction in absence of trauma
White (milky)	Chylothorax or cholesterol effusion
Brown	Long-standing bloody effusion; rupture of amebic liver abscess
Black^[1-4]	Aspergillus niger, Rhizomes oryzae, metastatic melanoma, pancreaticopleural fistula, crack cocaine use, bronchogenic adenocarcinoma, esophageal perforation during treatment with activated charcoal, chronic hemothorax
Yellow-green	Rheumatoid pleurisy
Dark green	Biliothorax
Color of:
Enteral tube feeding	Feeding tube has entered pleural space
Central venous catheter infusate	Extravascular catheter migration
Character of fluid
Pus	Empyema
Viscous	Mesothelioma
Debris	Rheumatoid pleurisy
Turbid	Inflammatory exudate or lipid effusion
Anchovy paste	Amebic liver abscess
Odor of fluid
Putrid	Anaerobic empyema
Ammonia	Urinothorax

References:

Chhabra A, Mukherjee V, Chowdhary M, et al. Black Pleural Effusion: A Unique Presentation of Metastatic Melanoma. Case Rep Oncol 2015; 8:222.
Huang TY, Tsai MJ. Education and imaging. Gastrointestinal: black pleural effusion induced by pancreaticopleural fistula. J Gastroenterol Hepatol 2013; 28:1798.
Jayakrishnan B, Dildar B, Rizavi DM, et al. Black pleural effusion. Lancet 2015; 386:e7.
Saraya T, Light RW, Takizawa H, Goto H. Black Pleural Effusion. Am J Med 2013; 126:641.e1.

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