What is the diagnostic approach for a patient presenting with fever?

From the Guidelines

The diagnostic approach for a patient presenting with fever should begin with a thorough history and physical examination to identify potential sources of infection or inflammation, as recommended by the most recent guidelines 1. The key elements of this approach include determining fever pattern, duration, associated symptoms, recent travel, exposures, and underlying medical conditions. Initial laboratory tests typically include complete blood count, basic metabolic panel, urinalysis, and blood cultures if systemic infection is suspected.

• Depending on clinical presentation, additional tests may include:
  • Chest X-ray
  • Inflammatory markers (C-reactive protein, erythrocyte sedimentation rate)
  • Liver function tests
  • Specific tests for suspected pathogens
• Imaging studies such as CT scans or ultrasound may be warranted if localized infection is suspected. For persistent fever of unknown origin, more extensive workup including specialized cultures, serologic testing, and sometimes tissue biopsy may be necessary.
• While antipyretics like acetaminophen (500-1000mg every 4-6 hours, maximum 4g daily) or ibuprofen (400-800mg every 6-8 hours with food) can provide symptomatic relief, they should not delay diagnosis of the underlying cause, as suggested by recent studies 1. The approach should be tailored to the patient's age, immune status, and clinical presentation, as fever represents the body's physiological response to various triggers, including infection, inflammation, malignancy, or drug reactions.
• Recent guidelines also recommend performing a chest radiograph for patients who develop fever during ICU stay 1, and considering CT scans for patients who have recently undergone thoracic, abdominal, or pelvic surgery 1.
• The use of 18F-fluorodeoxyglucose positron emission tomography/CT may be considered for critically ill patients with fever in whom other diagnostic tests have failed to establish an etiology 1.

From the Research

Diagnostic Approach for Fever

The diagnostic approach for a patient presenting with fever involves a thorough assessment, including a physical examination and evaluation of the patient's medical history and medications 2. The following steps can be taken:

• Evaluate each body system to match symptoms with a possible cause for fever
• Consider infection as a primary cause of fever
• Include noninfectious causes of fever in the differential diagnostic process
• Use laboratory tests, such as complete blood count, differential blood count, C-reactive protein, erythrocyte sedimentation rate, and procalcitonin, to aid in diagnosis, although these tests may not have sufficient sensitivity and specificity to definitively detect or rule out an infectious cause of fever 3, 4
• Obtain blood cultures if bacteremic or septic illnesses are suspected 3, 5

Evaluation of Fever in Specific Settings

In the emergency department, a structured approach to evaluating fever is essential, considering both infectious and non-infectious etiologies 4. In post-operative patients, there is a lack of consensus surrounding many common components of a fever evaluation, although physical examination and complete blood count are commonly agreed upon 6.

Considerations for Fever Evaluation

When evaluating fever, it is important to:

• Consider the clinical situation and patient population, such as elderly and immunocompromised patients, who may not always present with fever 3, 4
• Use core temperatures, such as rectal or oral temperatures, to accurately diagnose fever 3, 4
• Maintain a broad differential diagnosis to avoid pitfalls in fever evaluation 4