PURPOSE: Pleural effusion is a common diagnostic problem in clinical practice. Tuberculosis is the major cause of pleural effusion. Discerning tuberculous from nontuberculous pleural effusion is a greatest clinical challenge to the treating physician. Adenosine deaminase (ADA) is one of the Biochemical markers commonly used in the diagnosis of pleural effusion with its own limitations. Hence we studied the diagnostic significance of Pleural fluid Interferon Gamma (IFN-γ) in comparison with ADA in Tuberculous Pleural effusions.
METHODS: A total number of 50 patients presented with pleural effusion to AP Chest Hospital between MAY 2007 to OCT 2007 were taken in to the study. All the patients underwent detailed clinical evaluation, chest roentgenograms, Pleural fluid total and differential counts, Cytology, Biochemical analysis, Mycobacterial smear and culture and pleural biopsy. The ADA was assessed by calorimetric method and IFN-γ by Elisa. Out of the 50 patients, 31 (62%) had tuberculous pleurisy, among these 31 cases, 10 were HIV co-infected, 14 patients (28%) had malignant pleuritis and 5 patients (10%) had pleural effusion due to other etiologies.
RESULTS: The pleural fluid levels (mean±SE) of ADA (54.06±3.27 U/L Vs. 31±7.95 U/L, p<0.001) and IFN-γ (27.05±2.52IU/ml Vs. 1.90±1.53, p<0.00001) were significantly higher in tuberculous pleuritis than in non tuberculous pleuritis. At the cut off value of 3.7 IU/ml for IFN-γ and 40 U/L for ADA in differentiating tuberculous from non tuberculous effusions, it was found to have 96.77% sensitivity, 93.75% specificity, 96.77% positive predictive value, 93.75% negative predictive value for IFN-γ; and 83.87%, sensitivity 75% specificity, 86.67% positive predictive value, 70.59% negative predictive value for ADA.
CONCLUSION: The pleural fluid IFN-γ is the most sensitive, specific and useful marker for diagnosis of tuberculous pleural effusion compared to ADA. Diagnostic yield of both ADA and IFN-γ was independent of HIV co-infection.
CLINICAL IMPLICATIONS: IFN-γ assay, though expensive than ADA estimation, it is highly specific in differentiating Tuberculous from Non tuberculous effusions, especially Lymphomatous pleurisy. Further studies including larger numbers of patients are needed to verify this result.
DISCLOSURE: Subhakar Kandi, No Financial Disclosure Information; No Product/Research Disclosure Information