Adenosine Deaminase ( ADA) facts in tubercular pleural effusion

SOME FACT ABOUT ADA

• >ADA is an enzyme in purine salvage pathway that catalyzes the conversion of adenosine and deoxyadenosine to inosine and deoxyinosine
• >Abundant in activated T lymphocytes 
• >An ADA level >70 IU/L is highly suggestive of TB while a level < 40 IU/L virtually excludes the diagnosis of tuberculosis 
• >Meta-analysis of 40 studies from 1966 to 1999 showed the ADA sensitivity to vary between 47.1% to 100% and specificity between 0 to 100% 
• >Specificity increases when lymphocyte to neutrophil ratio in pleural fluid (>0.75) is considered in conjugation with an ADA concentration >50 IU/L 
• > In low prevalence setting (i.e. <1%) positive predictive value may be as low as 15% however negative predictive value increases 
• >In high prevalence of tuberculosis, ADA measurement is inexpensive, minimally invasive, rapid and readily accessible test that has sensitivity and specificity of 95% and 90% respectively 
• >Elevated ADA in lymphocyte rich pleural fluid has been reported in other diseases, such as rheumatoid arthritis, bronchoalveolar carcinoma, mesothelioma, mycoplasma and chlamydia pneumonia, psittacosis, paragonimiasis, infectious mononucleosis, brucellosis, mediterrianes fever, histoplasmosis, cocoidiodomycosis  and in most patient with empyema 
• >Two isoenzymes ADA1 and ADA2 
• >ADA1 is found in all cells with the highest activity observed in lymphocytes and monocytes.
• >ADA2 isoenzyme is predominantly found in monocytes/macrophages
• >ADA2 isoenzyme is primarily responsible for increase ADA activity in TB pleural effusion with a median contribution of 88% 
• >Pleural effusions with high ADA level and ADA1/total ADA ratio <0.45 makes the diagnosis of TB highly likely 
• >In immune compromised person ADA hold similar significance