TB is the commonest cause of pleural effusion (PE) its diagnosis remains obscured even after implication of available tools. ADA is an enzyme of purine metabolism (converts adenosine to inosine). It helps in differentiation of T-lymphocytes and maturation of monocytes. This study evaluated the usefulness of ADA in diagnosis and differentiation of tuberculous pleural effusion.MATERIAL AND METHODS: 356 patients of PE of varying etiology were included and divided into 5 groups: tuberculous PE (n=235), malignant PE (n=76), synpneumonic PE (n=21), transudative PE (n=9) & tuberculous PE with HIV infection (n=15). Diagnosis was established by pleural fluid, biochemical, microbiological and cytological analysis. Pleural biopsy was done in selected cases to establish the diagnosis (Abraham’s needle). ADA estimation was done (Giusti & Galani method, 1974) in both pleural fluid and serum.
This study revealed that in tuberculous pleural effusion ADA levels were significantly higher (Mean +SE : 102.09 +8.3, p<0.001) while other groups had lower values. None of the patients with tuberculous pleural effusion had a value <40 units/L. Sensitivity of ADA assay for diagnosis of tuberculous pleural effusion was 100% in contrast to 73.3% with positive biopsy, 68.6% with lymphocytic cytology and 56.6% with tuberculin test. Statistically, high significant difference between S. ADA values in TB effusion and other groups was observed (P<.001). Pleural fluid/serum ADA ratio was usually greater in patients with TB pleural effusion but low in patients with associated HIV infection hence of no diagnostic significance.
ADA activity may be useful parameter for diagnosis of tuberculous pleural effusion. Pleural fluid & serum ADA level were increased in these patients. Low levels serve to exclude TB and suggest the possibility of malignant effusion/parapneumonic effusion or associated HIV infection.CLINICAL INFECTION: Determination of ADA is easy and economic procedure. It is recommended that it should be done in all patients with pleural effusion, particularly, if diagnosis of TB is suspected and in low prevalence countries.
M. Vats, None.