Pleural fluid viscosity may help identifying malignant pleural effusions

Background and objective:  Cancer cells are larger in size and more rigid than blood cells. As the size and rigidity of cells contribute to blood viscosity, an association may exist between high pleural fluid viscosity and cancer cells in pleural effusions. The aim of this study was to determine the correlation between pleural fluid viscosity and cell constituents or laboratory data in pleural diseases with different aetiologies. Methods:  Fluid viscosities were determined in pleural effusions obtained via thoracocentesis. Pleural fluid viscosities were correlated with the laboratory data and with the percentages of different cellular constituents as assessed by cytological examination. Results:  Pleural fluid viscosity was highest in malignant pleural effusions with positive results on cytological examination, and was correlated with the percentages of tumour cells (Spearman's rho = 0.24, P = 0.037) and mitotic figures (rho = 0.23, P = 0.041) in the exudates. Multivariate logistic regression analysis showed that pleural fluid viscosity was a significant determinant of positive results on cytological examination (odds ratio (OR) 6.26, 95% confidence interval (CI) 1.32–29.8), as were the levels of protein (OR 1.48, 95% CI 1.01–2.16) and LDH (OR 1.001, 95% CI 1–1.002). Conclusion:  High pleural fluid viscosity may suggest a potential diagnosis of malignant pleural effusion.