Differential Diagnosis for Fever of Unknown Origin in Hospitalized Patients

Single Most Likely Diagnosis

• Hospital-acquired pneumonia: This is a common cause of fever in hospitalized patients, especially those who are intubated or have compromised respiratory function.
• Central line-associated bloodstream infection (CLABSI): Patients with central lines are at risk for developing bloodstream infections, which can cause fever.
• Urinary tract infection (UTI): UTIs are common in hospitalized patients, especially those with urinary catheters.

Other Likely Diagnoses

• Clostridioides difficile (C. diff) colitis: As mentioned, C. diff colitis is a common cause of fever in hospitalized patients, especially those who have received antibiotics.
• Gout: Although less common, gout can cause fever, especially if the patient has a severe flare-up or is experiencing a systemic reaction.
• Surgical site infection: Patients who have undergone surgery are at risk for developing surgical site infections, which can cause fever.
• Sinusitis: Hospitalized patients, especially those who are intubated or have nasal tubes, are at risk for developing sinusitis.

Do Not Miss Diagnoses

• Endocarditis: Although less common, endocarditis is a life-threatening condition that requires prompt diagnosis and treatment.
• Intra-abdominal infection (e.g., abscess, perforation): These conditions can be deadly if missed and require prompt surgical intervention.
• Meningitis: Hospitalized patients, especially those who are immunocompromised, are at risk for developing meningitis.
• Sepsis: Sepsis is a life-threatening condition that requires prompt recognition and treatment.

Rare Diagnoses

• Drug fever: Certain medications can cause fever, although this is a rare cause.
• Factitious fever: Some patients may intentionally or unintentionally manipulate their temperature readings, although this is a rare cause.
• Lymphoma or other malignancies: Although rare, certain types of cancer can cause fever, especially if the patient has a systemic infection or is experiencing tumor lysis syndrome.
• Autoimmune disorders (e.g., lupus, rheumatoid arthritis): These conditions can cause fever, although they are rare causes of fever in hospitalized patients.