Fever of Unknown Origin

Apply the classic FUO framework only when fever is at least 38.3°C (101°F) on at least two occasions, illness has persisted at least 3 weeks, the patient has no known immunocompromised state, and diagnosis remains uncertain after thorough history, examination, and baseline testing. PubMedPubMedOptimal use of the FDG-PET/CT in the diagnostic process of fever of unknown origin (FUO): a comprehensive review Do not apply this slower diagnostic pathway to neutropenic fever, hospital-acquired fever, or fever in a person with HIV; these categories have distinct pathogen risks and management priorities. ScienceDirect+2ScienceDirectFever of Unknown Origin: An Evidence-Based ReviewPubMedFebrile Neutropenia - StatPearls - NCBI BookshelfWileyAetiology of fever of unknown origin in people living with HIV: A ...

Screen immediately for neutropenic fever: a single oral temperature of at least 38.3°C or temperature of at least 38.0°C for at least 1 hour with absolute neutrophil count below 1,500 cells/µL meets the cited definition, while severe neutropenia is ANC below 500 cells/µL. PubMedPubMedFebrile Neutropenia - StatPearls - NCBI Bookshelf In a high-risk neutropenic patient, initiate broad-spectrum antibacterial management rather than prolonging an FUO evaluation; persistent fever after 4 to 7 days of broad-spectrum antibacterials with suspicion for fungal infection is an indication for empiric antifungal coverage. PubMedPubMedFebrile Neutropenia - StatPearls - NCBI Bookshelf

For apparent classic FUO, first verify the temperature record and review all prescription, over-the-counter, and recently discontinued medications for drug fever; also consider surreptitious thermometer manipulation when the evaluation remains unrevealing. PubMedPubMedFever of Unknown Origin - StatPearls - NCBI Bookshelf - NIH Reclassify any patient with a newly recognized immunocompromising condition, evolving organ dysfunction, or a focal syndrome, because that finding should redirect evaluation to the relevant acute syndrome rather than preserve an FUO label. ScienceDirect+1ScienceDirectFever of Unknown Origin: An Evidence-Based ReviewPubMedFever of Unknown Origin - StatPearls - NCBI Bookshelf - NIH

Repeat a complete history and physical examination rather than treating the first assessment as definitive. Potential diagnostic clues include localizing symptoms, physical findings, laboratory abnormalities, and imaging abnormalities that suggest a specific cause; these clues should determine targeted microbiology, cross-sectional imaging, endoscopy, echocardiography, or tissue sampling. PubMed+1PubMedFever of Unknown Origin - StatPearls - NCBI Bookshelf - NIHPubMedState of the art of 18F-FDG PET/CT application in inflammation and infection: a guide for image acquisition and interpretation Common etiologic categories remain infection, malignancy, and noninfectious inflammatory disease, but the working diagnosis should be a specific disease hypothesis rather than a broad category. ScienceDirect+1ScienceDirectFever of Unknown Origin: An Evidence-Based ReviewWileyFever of unknown origin in adults: 40 years on - Wiley Online Library

For classic FUO, document the baseline laboratory and microbiologic evaluation before escalating: ESR, CRP, platelet count, leukocyte count with differential, hemoglobin, electrolytes, creatinine, total protein, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, creatine kinase, ferritin, antinuclear antibodies, rheumatoid factor, protein electrophoresis, urinalysis, blood cultures, urine culture, and chest radiography. PubMedPubMedOptimal use of the FDG-PET/CT in the diagnostic process of fever of unknown origin (FUO): a comprehensive review This panel is not a substitute for localization; interpret abnormalities as branching points for focused imaging or biopsy. PubMed+1PubMedOptimal use of the FDG-PET/CT in the diagnostic process of fever of unknown origin (FUO): a comprehensive reviewPubMedState of the art of 18F-FDG PET/CT application in inflammation and infection: a guide for image acquisition and interpretation

Use inflammatory markers as activity signals rather than etiologic diagnoses. In one PET/CT FUO cohort, ESR above 20 mm/h, CRP above 0.8 mg/dL, and procalcitonin above 0.5 ng/mL were considered abnormal. PubMedPubMedDiagnostic Value of 18F-FDG-PET/CT in Patients with FUO - PMC FDG-PET/CT evidence is insufficient for FUO with normal CRP and ESR, so a normal inflammatory-marker profile should prompt reassessment of the fever pattern, medications, and noninflammatory explanations before proceeding to advanced metabolic imaging. PubMedPubMedEANM/SNMMI guideline/procedure standard for [18F]FDG hybrid PET use in infection and inflammation in adults v2.0

Direct targeted testing by pattern. New murmur, embolic phenomena, or persistent bacteremia should raise concern for endocarditis and support echocardiographic evaluation; echocardiography is also incorporated into many pre-PET FUO evaluations. PubMed+1PubMedDiagnostic Value of 18F-FDG-PET/CT in Patients with FUO - PMCWileyFever of Unknown Origin - Lamphier - 1980 - Wiley Online Library Pulmonary lesions require a focused infection-versus-malignancy assessment because lymphoma is reported as the most common malignant cause of FUO and may present with pulmonary lesions. WileyWileyEtiological distribution and clinical features of fever of unknown ... Myalgia with fever should retain adult-onset Still disease in the differential, particularly when the clinical syndrome supports it. WileyWileyAcute Adult‐Onset Still Disease Presenting as Fever of Unknown ...

Order FDG-PET/CT for FUO or inflammation of unknown origin when standard workup has not established a diagnosis. PubMedPubMedEANM/SNMMI guideline/procedure standard for [18F]FDG hybrid PET use in infection and inflammation in adults v2.0 The test can identify infection, inflammation, and malignancy because FDG accumulates in activated inflammatory cells and in neoplastic cells with increased glycolysis. PubMedPubMedState of the art of 18F-FDG PET/CT application in inflammation and infection: a guide for image acquisition and interpretation Its principal clinical value is not merely an abnormal scan: use focal uptake to choose targeted imaging, biopsy, or disease-specific treatment. PubMed+1PubMedEANM/SNMMI guideline/procedure standard for [18F]FDG hybrid PET use in infection and inflammation in adults v2.0PubMedState of the art of 18F-FDG PET/CT application in inflammation and infection: a guide for image acquisition and interpretation

Before PET/CT, ensure that routine clinical, hematologic, biochemical, serologic, culture, and chest-radiographic evaluation has been completed and that conventional imaging or echocardiography has addressed relevant clues. PubMed+1PubMedDiagnostic Value of 18F-FDG-PET/CT in Patients with FUO - PMCPubMedOptimal use of the FDG-PET/CT in the diagnostic process of fever of unknown origin (FUO): a comprehensive review In one FUO cohort, CT, MRI, echocardiography, endoscopy, bone-marrow biopsy, temporal-artery biopsy, and organ or lymph-node biopsy were frequently performed before or alongside PET/CT, illustrating that metabolic imaging complements rather than replaces directed anatomic evaluation. PubMedPubMedDiagnostic Value of 18F-FDG-PET/CT in Patients with FUO - PMC

If glucocorticoids are unavoidable, obtain FDG-PET/CT ideally within 3 days after oral glucocorticoid initiation. PubMedPubMedEANM/SNMMI guideline/procedure standard for [18F]FDG hybrid PET use in infection and inflammation in adults v2.0 When PET/CT identifies a lesion after a nondiagnostic CT-guided biopsy, use PET guidance to target the metabolically active portion of the lesion rather than repeating unguided sampling. PubMedPubMedAbstracts A negative FDG-PET/CT may support watchful waiting because it has been associated with favorable prognosis and spontaneous fever remission, but only after immediate threats and high-risk host states have been excluded. PubMedPubMedEANM/SNMMI guideline/procedure standard for [18F]FDG hybrid PET use in infection and inflammation in adults v2.0

In stable classic FUO, avoid empiric antituberculous drugs, broad antibacterial therapy, and glucocorticoids unless a specific clinical indication outweighs the loss of diagnostic clarity. Empiric therapy can obscure the underlying diagnosis and delay correct treatment, while prolonged undiagnosed FUO often has a favorable prognosis. ScienceDirectScienceDirectFever of Unknown Origin: An Evidence-Based Review This restraint does not apply to febrile neutropenia, in which immediate empiric antimicrobial therapy is central to management. PubMedPubMedFebrile Neutropenia - StatPearls - NCBI Bookshelf

For low-risk febrile neutropenia managed as an outpatient, the cited oral regimen is ciprofloxacin 500 to 750 mg every 12 hours plus amoxicillin/clavulanate 500 mg every 8 hours; clindamycin is listed as an alternative for penicillin allergy. PubMedPubMedFebrile Neutropenia - StatPearls - NCBI Bookshelf Admit if fever persists 48 to 72 hours. PubMedPubMedFebrile Neutropenia - StatPearls - NCBI Bookshelf In high-risk patients with persistent fever after 4 to 7 days of broad-spectrum antibacterial therapy and suspected fungal infection, add empiric antifungal coverage. PubMedPubMedFebrile Neutropenia - StatPearls - NCBI Bookshelf

Avoid using a rapid fall in CRP after glucocorticoids as confirmation of noninfectious inflammatory disease. In an elderly patient with inflammation of unknown origin, empiric prednisolone 30 mg/day normalized CRP but was associated with delayed malignancy diagnosis and severe glucocorticoid-related complications, including compression fracture and venous thromboembolism. Wolters KluwerWolters KluwerRisks of empiric glucocorticoid administration in... : Medicine Before initiating glucocorticoids for a presumed polymyalgia rheumatica-like syndrome or other inflammatory diagnosis, actively exclude malignancy and infection when the presentation is atypical or lacks confirmatory clues. Wolters KluwerWolters KluwerRisks of empiric glucocorticoid administration in... : Medicine

For patients without a diagnosis after targeted evaluation, establish a reassessment plan rather than repeating the same broad tests. At each recurrence or follow-up visit, repeat focused history and examination, compare CBC, differential, liver tests, creatinine, ESR, and CRP with prior values, and re-open tissue diagnosis if new lymphadenopathy, cytopenias, vascular symptoms, focal imaging abnormalities, or organ-specific signs emerge. The negative-PET/CT watchful-waiting approach is appropriate only if the patient remains clinically stable and the initial evaluation has excluded high-risk infectious and malignant signals. PubMed+2PubMedFever of Unknown Origin - StatPearls - NCBI Bookshelf - NIHPubMedEANM/SNMMI guideline/procedure standard for [18F]FDG hybrid PET use in infection and inflammation in adults v2.0PubMedState of the art of 18F-FDG PET/CT application in inflammation and infection: a guide for image acquisition and interpretation