Test Details: Adenosine Deaminase (ADA) deficiency is an autosomal recessive disorder of purine metabolism primarily affecting lymphocyte development, viability and function. ADA deficiency is the cause of 25-30 percent of Severe combined immunodeficiency (SCID) cases. It is increased in Tuberculosis because of the stimulation of T-cell lymphocytes by mycobacterial antigens. ADA estimation in fluid is helpful in differentiating tubercular from nontubercular etiology both in pulmonary and extra-pulmonary disease.