What is the most appropriate next investigation for a patient with rheumatoid arthritis experiencing recurrent knee inflammation?

In cases of rheumatoid arthritis with recurrent knee inflammation, it is essential to consider the possibility of septic arthritis, especially if the inflammation is acute or there are other concerning symptoms such as fever or increased pain. Blood cultures are crucial in these scenarios as they help determine if there is a systemic infection present that could be contributing to the joint symptoms.

While serum CRP can indicate inflammation and serum urate can evaluate for gout, these tests do not specifically assess for infection. The testing of synovial fluid culture is also important in diagnosing infections within the joint, but it typically follows initial blood cultures to confirm the presence of infection. Therefore, starting with blood cultures when there is a concern for infection is a rational initial step in the evaluation of recurrent knee inflammation in a patient with rheumatoid arthritis.