What are the differential diagnoses for fever (pyrexia)?

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Last updated: May 25, 2025 • View editorial policy

Fever Differential Diagnosis

The differential diagnosis for fever is extensive and can be categorized into several groups. Here's a breakdown of the possible causes:

  • Single Most Likely Diagnosis + Viral upper respiratory tract infection: This is often the most common cause of fever, especially in otherwise healthy individuals. Justification: The high prevalence of viral infections, such as the common cold or flu, makes this a likely diagnosis.
  • Other Likely Diagnoses + Bacterial pneumonia: Fever is a common symptom of pneumonia, especially in older adults or those with underlying health conditions. Justification: The presence of fever, cough, and shortness of breath increases the likelihood of this diagnosis. + Urinary tract infection: Fever can be a symptom of a UTI, particularly in women or individuals with underlying urological conditions. Justification: The combination of fever, dysuria, and flank pain suggests a UTI. + Gastroenteritis: Fever can occur with viral or bacterial gastroenteritis, often accompanied by diarrhea and vomiting. Justification: The presence of fever, abdominal cramps, and changes in bowel habits supports this diagnosis.
  • Do Not Miss Diagnoses + Sepsis: A life-threatening condition that requires prompt recognition and treatment. Justification: Fever, tachycardia, and hypotension can indicate sepsis, making it crucial to consider this diagnosis. + Meningitis: A serious infection that can cause fever, headache, and stiff neck. Justification: The combination of fever, headache, and neck stiffness warrants immediate attention and evaluation for meningitis. + Endocarditis: An infection of the heart valves that can cause fever, especially in individuals with a history of heart disease. Justification: Fever, heart murmur, and embolic phenomena increase the suspicion for endocarditis.
  • Rare Diagnoses + Lymphoma: Some types of lymphoma can cause fever, often accompanied by weight loss and night sweats. Justification: Although rare, lymphoma should be considered in individuals with persistent, unexplained fever. + Tuberculosis: A chronic infection that can cause fever, especially in individuals with a history of exposure or immunocompromised states. Justification: Fever, weight loss, and cough in a high-risk individual may suggest tuberculosis. + Autoimmune disorders: Certain autoimmune conditions, such as lupus or rheumatoid arthritis, can cause fever. Justification: A thorough evaluation of symptoms and laboratory results is necessary to diagnose these rare conditions.

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