For collection of pleural fluid, the procedure of pleural tap or thoracocentesis has to be preformed. It helps to drain the fluid in the costo-diaphragmatic recess and the effuse collected is further used for various tests. Usually the patient is not sedated during the procedure and either is in sitting position or in supine position. An X-Ray might be taken to ascertain the position to insert the needle. Usually the needle is inserted at the level of the eighth intercostal space.On thoracocentesis, pleural fluid is found to be typically straw-colored. The characteristic observation is a high protein content with marked lymphocytosis, although lower protein content may be found in patients with AIDS. The presence of a large number of mesothelial cells (more than 1% of white blood cells) and eosinophils (more than 10%) is strong evidence against the diagnosis of tuberculosis. Pleural fluid pH is usually higher than 7.3, and pleural fluid glucose concentration is not significantly decreased. ADA is an enzyme catalyzing the deamination reaction from adenosine to inosine. It is also an essential enzyme of the purine catabolic pathway. There are 2 isoforms of ADA, ADA-1 and ADA-2. ADA-1 is found in many tissues including red blood cells. ADA-2 is found only in macrophages and monocytes ADA acts in proliferation and differentiation of lymphocyte, especially T lymphocyte. It also acts in maturation of monocytes transforming them to macrophage. ADA is a significant indicator of active cellular immunity. It increases in biological fluids in the course of infectious disease characterized by micro-organisms infecting the macrophages.The samples are taken and centrifuged and ADA levels have to be measured by ADA kit (manufactured by- ____________________ and cost is Rs. 9000). Total plasma ADA can be measured by a spectrophotometric method described by Guisti and Galanti in 1984. It uses the principles that the ADA assay is based on the enzymatic deamination of adenosine to inosine and formation of ammonia. Ammonia (NH3) forms under conversion of adenosine causing an intensely blue indophenol with sodium hypochlorite and phenol in an alkaline solution as determined by modification of a Berthelot’s reaction. Sodium nitroprusside is used as the catalyst. The ammonia concentration is directly proportional to the absorbance of the indophenols measured at a wavelength of 620 nm (red band filter). The reaction catalyzed by ADA is stopped at the end of one hour incubation at 37ºC by the addition of phenol nitroprusside solution. ADA activity is expressed in international units (IU) using the formula as follows: (Absorbance of sample/ Absorbance of standard) x 50 IU/l 10.Measurement of Sensitivity and Specificity of the Diagnostic Procedure:Sensitivity: It represents the probability that a test result will be positive when the disease is present (true positive rate). = a / (a+b)Specificity: It represents the probability that a test result will be negative when the disease is not present (true negative rate). = d / (c+d)where a represents –No of cases in diseased group are positive . b represents -No of cases in the diseased group are negative. c represents -No of cases in the non diseased group are positive. d represents -No of cases in the non-diseased group are negative.Both specificity and sensitivity are expressed in percentages. The specificity and sensitivity in the study was done by an online calculator resource developed by a Belgian software developer ,MedCalc Software.