Handy Guide to Fever Diagnosis for Doctors with Quick Diagnosis table PDF Download Link

Hey there! Fever is a common sign that can point to a variety of conditions, from harmless viral infections to serious illnesses. Knowing what’s causing your fever is crucial for getting the right treatment at the right time. This article is a handy guide for doctors on how to diagnose fever, with tips on how to rule out different possibilities based on your symptoms and tests that can help confirm the diagnosis.

Fever is typically defined as a body temperature greater than 38°C (100.4°F), measured orally. It is a physiological response often caused by an infection or inflammation. However, fever can also result from non-infectious causes, such as malignancies, autoimmune diseases, and drug reactions.

For physicians, evaluating a fever involves:

1. Assessing the duration of the fever (acute, subacute, or chronic).
2. Understanding the fever pattern (intermittent, remittent, continuous, or relapsing).
3. Conducting a comprehensive patient history and physical examination.
4. Identifying the most likely causes based on the clinical presentation.

Types of Fever Based on Duration and Patterns:

1. Acute Fever:
   • Duration: Less than 7 days.
   • Common Causes: Acute infections, drug-induced fever, heat stroke.
   • Key Tests: Blood cultures, Complete Blood Count (CBC), chest X-ray (for pneumonia), and urinalysis.
2. Subacute Fever:
   • Duration: 7 to 14 days.
   • Common Causes: Tuberculosis, endocarditis, Brucellosis, and some viral infections (e.g., Epstein-Barr Virus).
   • Key Tests: Chest X-ray, blood cultures, PCR for specific viral or bacterial pathogens, Tuberculin Skin Test (TST), and blood serology.
3. Chronic Fever:
   • Duration: More than 14 days.
   • Common Causes: Chronic infections (e.g., HIV, tuberculosis), autoimmune diseases (e.g., systemic lupus erythematosus), and malignancies.
   • Key Tests: Serology for chronic infections, biopsy for suspected malignancies, imaging (CT, MRI), and autoimmune panels.

Approach to Fever Diagnosis:

1. Infectious Causes of Fever:

Infections remain one of the most common causes of fever, and physicians need to differentiate between bacterial, viral, parasitic, and fungal infections. Below are common infectious causes and their diagnostic approach:

A. Bacterial Infections:

1. Typhoid Fever (Salmonella typhi):
   • Symptoms: Prolonged high fever, headache, abdominal pain, constipation, and sometimes diarrhea.
   • Diagnostic Tests: Blood cultures, Widal test (for Salmonella antibodies), stool culture, and urine culture.
2. Tuberculosis (TB):
   • Symptoms: Persistent cough, night sweats, weight loss, hemoptysis (coughing up blood).
   • Diagnostic Tests: Chest X-ray, sputum smear for acid-fast bacilli (AFB), tuberculin skin test (TST), PCR for Mycobacterium tuberculosis.
3. Pneumonia:
   • Symptoms: Cough, pleuritic chest pain, difficulty breathing, and productive cough.
   • Diagnostic Tests: Chest X-ray, sputum culture, blood cultures, CBC (to assess for leukocytosis), and urine antigen tests for pneumococcus or Legionella.
4. Sepsis:
   • Symptoms: Fever, hypotension, tachycardia, confusion, and signs of organ dysfunction.
   • Diagnostic Tests: Blood cultures, CBC, lactate level, renal and liver function tests, and imaging to identify the source of infection.

B. Viral Infections:

1. Influenza:
   • Symptoms: Sudden onset of fever, chills, body aches, sore throat, cough, and fatigue.
   • Diagnostic Tests: Rapid antigen testing (e.g., influenza A/B), PCR for influenza, and throat swab.
2. COVID-19:
   • Symptoms: Fever, dry cough, shortness of breath, loss of taste or smell, fatigue, and muscle aches.
   • Diagnostic Tests: RT-PCR for SARS-CoV-2, rapid antigen tests, and chest X-ray/CT scan for lung involvement.
3. Dengue Fever:
   • Symptoms: High fever, retro-orbital headache, muscle and joint pain, rash, and hemorrhagic manifestations.
   • Diagnostic Tests: Dengue NS1 antigen test, Dengue IgM/IgG antibodies, and platelet count.

C. Parasitic Infections:

1. Malaria:
   • Symptoms: Fever with chills, sweating, fatigue, nausea, and anemia.
   • Diagnostic Tests: Peripheral blood smear (for Plasmodium species), rapid antigen tests, and PCR for malaria.
2. Leishmaniasis:
   • Symptoms: Fever, weight loss, enlarged spleen, and liver.
   • Diagnostic Tests: PCR, serology for Leishmania, bone marrow biopsy for parasite detection.

D. Fungal Infections:

1. Histoplasmosis:
   • Symptoms: Fever, cough, chest pain, and fatigue, often in immunocompromised patients.
   • Diagnostic Tests: Fungal cultures, urine and serum antigen tests, chest X-ray/CT scan, and PCR.
2. Coccidioidomycosis:
   • Symptoms: Fever, cough, chest pain, night sweats, and weight loss.
   • Diagnostic Tests: Fungal cultures, serology (IgM and IgG antibodies), and chest X-ray.

2. Non-Infectious Causes of Fever:

Non-infectious causes of fever are often challenging to diagnose, as they may mimic infectious diseases. Here are key non-infectious conditions and their diagnostic approaches:

A. Autoimmune and Inflammatory Diseases:

1. Systemic Lupus Erythematosus (SLE):
   • Symptoms: Butterfly-shaped facial rash, photosensitivity, joint pain, fatigue, and renal involvement.
   • Diagnostic Tests: ANA (antinuclear antibody) test, anti-dsDNA antibodies, ESR, and C-reactive protein (CRP).
2. Rheumatoid Arthritis (RA):
   • Symptoms: Morning stiffness, joint pain, swelling, and fatigue.
   • Diagnostic Tests: Rheumatoid factor (RF), anti-citrullinated peptide antibodies (anti-CCP), ESR, and CRP.
3. Vasculitis (e.g., Giant Cell Arteritis, Takayasu’s Arteritis):
   • Symptoms: Fever, weight loss, fatigue, muscle aches, and organ-specific symptoms depending on vessel involvement.
   • Diagnostic Tests: ESR, CRP, biopsy of affected tissues (e.g., temporal artery biopsy for giant cell arteritis), and angiography.

B. Malignancies:

1. Lymphoma (Hodgkin and Non-Hodgkin):
   • Symptoms: Fever, night sweats, weight loss, fatigue, and lymphadenopathy.
   • Diagnostic Tests: Lymph node biopsy, PET-CT, CBC, and lactate dehydrogenase (LDH) levels.
2. Leukemia:
   • Symptoms: Fever, pallor, fatigue, bleeding, and enlarged spleen or liver.
   • Diagnostic Tests: Bone marrow biopsy, CBC with peripheral blood smear, and flow cytometry.

C. Drug-Induced Fever:

• Symptoms: Fever often develops days to weeks after starting a new medication. It may be accompanied by rash or joint pain.
• Diagnostic Tests: Drug history, CBC, liver and renal function tests, and discontinuation of suspected drugs to assess response.

3. Investigations for Fever of Unknown Origin (FUO):

If the fever persists beyond three weeks and the cause remains unclear after a thorough history and physical examination, further testing is required. The classic triad of FUO includes:

• Fever: Persistent for more than 3 weeks.
• Absence of a definitive diagnosis after 1 week of inpatient investigation.
• No response to treatment after 1 week.

Diagnostic Approach for FUO:

1. Extensive Blood Work: CBC, liver and renal function tests, CRP, ESR, blood cultures.
2. Imaging: Chest X-ray, abdominal ultrasound, or CT scan.
3. Specific Tests: Depending on the suspected etiology, tests for tuberculosis, HIV, malaria, and other infections.
4. Tissue Biopsy: If malignancy, autoimmune diseases, or other diseases are suspected, tissue biopsy (e.g., lymph node biopsy) may be needed.

Fever is a common but complex clinical sign that requires a structured approach to diagnosis. By considering the duration, pattern, and associated clinical signs, physicians can narrow down the list of potential causes. In addition to a detailed history and physical examination, diagnostic tests—ranging from blood cultures to imaging studies—play a crucial role in confirming the diagnosis and determining the underlying cause.

Timely and accurate identification of the cause of fever is essential for effective treatment, whether the fever is due to an infection, an autoimmune disease, a malignancy, or a drug reaction. This comprehensive diagnostic approach ensures better patient outcomes and helps prevent misdiagnosis and unnecessary treatments.