2011 Dec - The use of pleural fluid deaminase (ADA) and C-reactive protein (CRP) in the diagnostic workup of tuberculous pleural effusion
Dr Donald Kam-Kwok SHING, Pulmonary and Palliative Care Service, Department of Medicine, Haven of Hope Hospital
Background
Tuberculous pleural effusion is a diagnostic challenge to physicians. Biomarkers have been developed for diagnostic workup. Pleural fluid ADA level has been widely studied but local clinical study on the currently using Diazyme ADA assay is not available. Pleural fluid CRP level has been shown to be useful in diagnosis of tuberculous pleural effusion. Combined use of these two markers may improve the diagnostic performance.
Methods
This was a prospective study. Consecutive patients attended to respiratory units of Haven of Hope Hospital and United Christian Hospital from August 2010 to July 2011 for pleural tapping were recruited. Pleural fluid was sent for ADA and CRP assay in all patients. Records of patient were reviewed for demographic data, clinical diagnoses and pleural fluid results.
Results
173 patients were recruited, including 38 tuberculous pleural effusion, 58 malignant pleural effusion, 19 parapneumonic pleural effusion, 47 transudative pleural effusion and others. Mean pleural fluid ADA levels were 41.1, 11.0, 17.7 and 5.5 U/L respectively. Optimal cut-off value for diagnosing tuberculous pleural effusion was >18.5 U/L, with sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (LR+), negative likelihood ratio (LR-), area under curve (AUC) of 94.7%, 90.6%, 75%, 98.3%, 10.1, 0.06, 0.975 (95% CI 0.954-0.996) respectively. Median pleural fluid CRP levels were 21.5, 6.9, 29.7, and 3.3 mg/L respectively. Optimal cut-off value for diagnosing tuberculous pleural effusion was >11.6 mg/L, with sensitivity, specificity, PPV, NPV, LR+, LR-, AUC of 86.8%, 67.7%, 44.6%, 94.5%, 2.7, 0.19, 0.773 (95% CI 0.698-0.848) respectively. Using pleural fluid ADA and CRP together improved the diagnostic performance further, especially when applying to lymphocytic pleural effusion. ADA level and cut-off value were low when compared to historical studies.
Conclusion
Pleural fluid ADA is an excellent test for diagnosis of tuberculous pleural effusion. Using pleural fluid ADA and CRP together improved the performance further, especially when applying to lymphocytic pleural effusion.
