What is the approach to assessing a patient with fever?

Assessment of the Patient with Fever

A new fever in any patient should trigger a targeted clinical assessment guided by the patient's setting and risk factors, rather than reflexive ordering of laboratory tests and imaging studies. 1

Initial Clinical Evaluation

Begin with a focused assessment that includes:

• Respiratory rate measurement – A respiratory rate >25 breaths/min has 90% sensitivity and 95% specificity for pneumonia in long-term care residents 1
• Mental status changes – Altered mentation may indicate aspiration pneumonia, sepsis, or CNS infection 1
• Hydration status – Assess for signs of dehydration which may complicate infection 1
• Medication review – Specifically evaluate for antibiotics or chemotherapy within the past 60 days, as these predispose to C. difficile infection and drug fever 1, 2
• Recent procedures and surgeries – Document any thoracic, abdominal, or pelvic operations, as well as indwelling devices (catheters, prosthetic joints, central lines) 1, 2

Systematic Physical Examination

Direct attention to the most common infection sources:

• Oropharynx and conjunctiva – Examine for pharyngitis, dental abscess, or conjunctivitis 1
• Chest auscultation – Listen for crackles, decreased breath sounds, or consolidation 1
• Skin examination – Turn the patient to inspect for pressure ulcers, surgical site infections, and cellulitis, particularly in the sacral, perineal, and perirectal areas 1, 2
• Cardiac examination – Assess for new murmurs suggesting endocarditis 1
• Abdominal examination – Palpate for tenderness, organomegaly, or peritoneal signs 1
• Indwelling device sites – Inspect all catheter insertion sites for erythema, purulence, or tenderness 1, 2

Risk Factor Assessment

Identify predisposing conditions that guide your differential:

• Diabetes mellitus – Increases risk for skin infections and urinary tract infections 1
• COPD – Predisposes to pneumonia 1
• Poor swallowing/gag reflex – Raises concern for aspiration pneumonia 1
• Indwelling urinary catheter – Associated with 39-fold increased risk of bacteremia 1
• Prosthetic devices – Consider septic arthritis in patients with artificial joints 1
• Chronic immobility – Evaluate for pressure ulcers 1

Core Diagnostic Studies

After clinical assessment, obtain targeted testing:

Imaging

• Chest radiograph – Obtain in all febrile patients, as pneumonia is the most common infection causing fever in hospitalized patients 1, 2
• CT imaging – Perform for patients with recent thoracic, abdominal, or pelvic surgery if initial workup does not identify an etiology 1, 2
• Abdominal ultrasound – Obtain formal bedside ultrasound if patient has abdominal symptoms, abnormal physical exam, or elevated transaminases/alkaline phosphatase/bilirubin 1

Microbiologic Studies

• Blood cultures – Collect at least two sets (ideally 60 mL total) from different anatomical sites simultaneously, without time interval between them 1, 2
• Central line cultures – If central venous catheter present, draw simultaneously from catheter and peripheral site to calculate differential time to positivity; sample at least two lumens 1, 2
• Respiratory specimens – Obtain lower respiratory tract sample (sputum, tracheal aspirate, or bronchoalveolar lavage) before antibiotic initiation if pneumonia suspected 1, 2
• Urine culture – Only if pyuria present and UTI suspected; replace urinary catheter first and culture from newly placed catheter 1, 2
• Stool testing – Test for C. difficile toxin if diarrhea present and patient received antibiotics/chemotherapy within 60 days 1, 2

Viral Testing

• Respiratory viral panel – Consider viral nucleic acid amplification testing if patient has new cough or upper respiratory symptoms 1, 2

Temperature Measurement Considerations

Use the most accurate method available:

• Preferred methods – Pulmonary artery catheter thermistor, bladder catheter thermistor, or esophageal probe provide core temperature readings 1, 2
• Rectal temperature – More accurate than oral or axillary methods in long-term care residents 1
• Electronic thermometry – Superior to standard mercury thermometry 1
• Avoid – Axillary, tympanic, or temporal artery measurements when core temperature assessment is critical 2

Temperature Thresholds

Different populations require different fever definitions:

• Long-term care residents – Temperature ≥100°F (37.8°C) has 55% positive predictive value for infection; alternatively, temperature increase ≥2°F (1.1°C) over baseline, or oral temperature ≥99°F (37.2°C), or rectal temperature ≥99.5°F (37.5°C) on repeated measurements 1
• General hospitalized patients – Temperature >38.3°C (100.9°F) typically used as threshold 1

Advanced Evaluation for Unclear Source

If initial workup fails to identify etiology:

• 18F-FDG PET/CT – Consider if transport risk acceptable; has sensitivity of 85-100% for identifying occult infection 1, 2
• Thoracic ultrasound – May identify pleural effusions and parenchymal pathology if chest radiograph abnormal and expertise available 1, 2

Biomarkers

Use selectively based on pretest probability:

• Procalcitonin or CRP – Measure when bacterial infection probability is low-to-intermediate, in addition to clinical evaluation 2
• Do not use – PCT or CRP to rule out infection when bacterial infection probability is high 2

Critical Pitfalls to Avoid

• Avoid automatic order sets – Let clinical assessment guide testing rather than reflexively ordering all possible cultures and imaging 1
• Do not culture urine routinely – Avoid urine cultures in catheterized patients without pyuria or UTI symptoms 2
• Do not send stool cultures routinely – Only culture stool if patient admitted with diarrhea, is HIV-positive, or part of outbreak investigation 1
• Consider noninfectious causes – Drug fever, venous thrombosis, pulmonary embolism, acute MI, pancreatitis, and malignancy can all present with fever 1
• Recognize atypical presentations – Elderly and immunocompromised patients may have serious infections without fever 3

Special Considerations by Setting

Long-Term Care Facilities

• Geriatric nurse practitioners can enhance identification of acute problems including fever, though they do not alter overall functional outcomes 1
• Certified nursing assistants often miss infections, attributing symptoms to "colds" when pneumonia, UTI, or skin infections are present 1

Intensive Care Unit

• Not all fevers require investigation – Obvious noninfectious causes (immediate postoperative fever) do not mandate workup 1
• Fever has many noninfectious causes in ICU patients including drug reactions, venous thrombosis, acalculous cholecystitis, and cytokine release syndrome 1