Quantitation of cholesterol in body fluids is clinically important and relevant in particular to the diagnosis of a cholesterol effusion. Cholesterol effusions (also known as pseudochylothorax or chyliform effusion) are important to differentiate from chylothorax, as their etiologies and therapeutic management strategies differ. Pseudochylous or chyliform effusions accumulate gradually through the breakdown of cellular lipids in long-standing effusions such as rheumatoid pleuritis, tuberculosis, or myxedema and by definition the effluent contains high concentrations of cholesterol. The fluid may have a milky or opalescent appearance and be similar to that of a chylous effusion, which contains high concentrations of triglycerides in the form of chylomicrons. An elevated cholesterol >250 mg/dL defines a cholesterol effusion in pleural fluid.
Ascites is the pathologic accumulation of excess fluid in the peritoneal cavity. Cholesterol analysis in peritoneal fluid may be a useful index to separate malignant ascites (>45-48 mg/dL) from cirrhotic ascites. Using a cutoff value of 48 mg/dL, the sensitivity, specificity, positive and negative predictive value, and overall diagnostic accuracy for differentiating malignant from nonmalignant ascites were reported as 96.5%, 96.6%, 93.3%, 98.3%, and 96.6%, respectively.(1)
Normal synovial fluid contains extremely low concentrations of lipids. Abnormalities in synovial fluid lipids may be attributed to cholesterol-rich pseudochylous effusions which may be associated with chronic rheumatoid arthritis, lipid droplets due to traumatic injury and rarely due to severe chylous effusions associated with systemic lupus erythematosus, filariasis, pancreatitis, and trauma.(1) However, these diseases can usually be differentiated clinically and by gross and microscopic examination; quantification of lipids in synovial fluid only provides supporting information to the clinical picture.
Distinguishing between chylous and nonchylous effusions
Identifying iatrogenic effusions
This test cannot be performed on viscous fluids.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. McPherson RA, Matthew RP, Henry JB: Cerebrospinal, Synovial, and Serous Body Fluids. In Henry's Clinical Diagnosis and Management by Laboratory Methods. Philadelphia, Saunders Elsevier, 2007, pp 426-454
2. Valdes L, Pose A, Suarez J, et al: Cholesterol: a useful parameter for distinguishing between pleural exudates and transudates. Chest 1991;99:1097-1102
3. Tietz Textbook of Clinical Chemistry. Third edition. Edited by CA Burtis, ER Ashwood, WB Saunders, Philadelphia, 1999, pp 1130, 1767-1770
4. Ellefson RD, Elveback L, Weidman W: Plasma lipoproteins of children and youths in Rochester, MN. DHEW Publication No. (NIH) 1978;78-1472