Answer: To differentiate between malignant and tuberculous pleurisy
If a situation arises where the pleural fluid is exudative, lymphocytic, but initial cytology, smear, and culture fails to document tuberculosis or malignancy, ADA can be relied on with good confidence. The usual cutoff point to make that distinction is at around 35-40 U/L. ADA is usually less than 40 U/L in malignant pleural effusions, more than 35 to 50 U/L in tuberculous pleural effusions.
Said that interpretation of ADA should be done in connection with clinical history, physical exam, geographic locations, and local experts.
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