Blood tests
Blood tests help to confirm if there is an infection and find out the cause of the infection (bacterial or viral). Blood tests also help to check if there is any problem with the immune system of the patient. They check for an autoimmune disorder such as arthritis [1], lupus [2], and rheumatoid [3], where the initial symptoms can be pleurisy.
Thoracentesis
Thoracentesis involves the doctor inserting a needle into a specific location in the chest where imaging tests detect fluid. Then, the doctor removes the fluid and tests it for the presence of infections.
Thoracentesis is an invasive test and it has so many associated risks, so it is rarely done for patients with just pleurisy.