The definitive help to diagnose an effusion, and distinguish between a transudate and an exudate, and thus help distinguish infection from heart disease, is a throacentesis, for diagnostic and sometimes therapeutic purposes.
This fluid drawn from the thoracic space is sent to the lab for analysis.
One can keep guessing and treating, but this has already happened, and it is time for a proper diagnosis.
Any good internal medicine doctor, or pulmonologist can do this, which would involve a brief stay in observation in the hospital.
Talk to his doctors about this possibility.
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