Pyrexia of Unknown Origin (PUO) Workup

Modified Petersdorf criteria: temperature ≥38.3°C on multiple occasions + duration ≥3 weeks + no diagnosis after 1 week of inpatient investigation OR 3 outpatient visits / 3 days inpatient. Categories: • Classic (immunocompetent). • Healthcare-associated. • Neutropenic (separate pathway). • HIV-associated. Common causes (Western series): • Infection (~30%): TB, abscess (intra-abdominal), endocarditis, urinary, viral. • Malignancy (~20%): lymphoma, RCC, hepatic metastases, leukaemia. • Non-infectious inflammatory (~20%): vasculitis (especially GCA in elderly), adult-onset Still's, sarcoid, IBD, drug fever. • Miscellaneous + undiagnosed (~30%).