What are the additional diagnostic tests for a patient with prolonged fever?

For a patient presenting with prolonged fever, I recommend starting with a comprehensive diagnostic workup that includes complete blood counts, blood cultures, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and tests for tuberculosis and other infections. Additionally, measuring the levels of Immunoglobulin A (IgA) could help in diagnosing conditions like selective IgA deficiency. Imaging studies such as chest X-rays, abdominal ultrasounds, or CT scans may be necessary to rule out structural abnormalities or malignancies. Empirical antibiotic treatment may be considered based on clinical judgment, pending culture results, with a broad-spectrum antibiotic like ceftriaxone being a potential option. If an autoimmune condition like juvenile idiopathic arthritis is suspected, referral to a pediatric rheumatologist for further evaluation and potential initiation of anti-inflammatory medications like naproxen or methotrexate may be necessary. Second-line interventions may include more targeted therapies based on specific diagnoses, such as antitubercular therapy if tuberculosis is confirmed, or disease-modifying antirheumatic drugs (DMARDs) for autoimmune conditions. Given the potential for significant morbidity and mortality, close monitoring and timely adjustment of the treatment plan based on the patient's response are essential.