Value of D-dimer and alkaline phosphatase in the diagnosis of pleural effusion

IntroductionPleural effusion is a common clinical presentation in several diseases. Various parameters from pleural fluid have been studied to identify the cause of effusion. D-dimer is a degradation product of cross-linked fibrin and alkaline phosphatase (ALP) is one of the biochemical markers found in pleural effusion. ALP is a plasma membrane derived enzyme of uncertain physiologic function that hydrolyzes synthetic phosphate esters at pH 9. It is present in the serum in several forms, i.e., ALP-1 alpha 2, ALP-2 beta 1 and ALP-3 beta 2.AimThe present study was carried out to evaluate the value of alkaline phosphatase and D-dimer concentration in the pleural effusions and serum as a diagnostic tool.MethodsThis study was carried out on one hundred patients with pleural effusions of different aetiologies. 75 patients had exudative pleural effusions (35 patients had tuberculous effusion, 20 patients had malignant effusion, 10 had parapneumonic effusion, 5 had empyema and 5 patients had systemic lupus erythematosis) and 25 patients had transudative effusions (20 patients had hepatic and 5 patients had cardiac effusions). Serum and pleural effusion D-dimer (measured by ELISA), ALP, LDH and protein levels were measured.ResultsThere was a highly significant difference in the pleural fluid D-dimer and ALP levels between exudative and transudative effusions (P < 0.001). Also, there was a highly significant difference in both the pleural fluid D-dimer and ALP levels between tuberculous and non tuberculous pleural effusions (P < 0.001). There were no significant differences in the pleural levels of either the D-dimer or the ALP between malignant and non malignant pleural effusions (P > 0.05). Lastly there was no significant difference (P > 0.05) in the serum levels of either the ALP or the D-dimer between different types of effusions.ConclusionMeasurement of pleural fluid D-dimer and ALP levels aids in the differentiation between exudative and transudative pleural effusions. Also, both pleural fluid D Dimer and ALP are significantly higher in tuberculous pleural effusions.