What are the important considerations in the workup of a patient with a suspected respiratory infection, including medications, indications, labs, and vitals?

Important Considerations in the Workup of a Patient with Suspected Respiratory Infection

The most important considerations in the workup of a patient with suspected respiratory infection include obtaining a chest radiograph, appropriate laboratory tests including complete blood count, and respiratory specimens for microbiological evaluation before initiating antimicrobial therapy. 1

Clinical Assessment

• Assess for suggestive symptoms and signs of pneumonia including cough, dyspnea, pleural pain, fever ≥38°C, sweating/shivers, aches and pains, tachypnea, and new and localizing chest examination signs 1
• Evaluate vital signs, particularly respiratory rate, oxygen saturation, temperature, and blood pressure to determine severity of illness and need for hospitalization 1
• Note that the absence of runny nose and presence of breathlessness, crackles, diminished breath sounds, tachycardia, and fever are particularly suggestive of pneumonia 1
• Consider severity assessment tools such as CURB-65 score (Confusion, Urea >7 mmol/L, Respiratory rate ≥30/min, Blood pressure [SBP <90 mmHg or DBP ≤60 mmHg], Age ≥65 years) to guide management decisions 1

Imaging Studies

• Obtain a chest radiograph in all patients with suspected respiratory infection seen in the hospital setting to improve diagnostic accuracy and define severity 1
• Consider posterior-anterior and lateral views when possible, as portable chest radiographs have limited accuracy 1
• Look for multilobar involvement, pleural effusions, or cavitation which may indicate greater severity or complications 1
• For patients with ARDS, additional imaging may be needed as it is difficult to demonstrate deterioration on radiographic images 1

Laboratory Investigations

• Obtain the following tests for all patients with suspected respiratory infection requiring hospital evaluation: 1

  • Full blood count (to assess for leukocytosis or leukopenia)
  • Urea and electrolytes (to assess renal function and for CURB-65 scoring)
  • Liver function tests
  • C-reactive protein (CRP) measurement (values ≥30 mg/L increase likelihood of pneumonia) 1
  • Pulse oximetry (if <92% on air, obtain arterial blood gases) 1

• Consider additional tests based on clinical presentation: 1

  • Blood cultures (before antibiotic administration) for suspected pneumonia
  • Sputum cultures for Gram stain and culture
  • Respiratory viral testing including COVID-19 evaluation per institutional guidelines 1
  • Legionella and pneumococcal urinary antigen tests for severe pneumonia 1

Microbiological Evaluation

• Obtain samples of lower respiratory tract secretions before antibiotic changes 1
• Collect blood cultures in all patients with suspected pneumonia requiring hospitalization 1
• Consider diagnostic thoracentesis if significant pleural effusion is present 1
• Note that routine microbiological testing may not be necessary for outpatients with non-severe suspected respiratory infections 1
• A sterile culture of respiratory secretions in the absence of new antibiotics in the past 72 hours virtually rules out bacterial pneumonia 1

Medication Considerations

• Review current medications, particularly immunosuppressive agents that may increase risk of opportunistic infections 1
• Consider whether the patient is on immune checkpoint inhibitors, which can cause immune-related pulmonary reactions that may mimic infection 1
• Assess for medications that might affect respiratory function, such as beta-blockers which may block bronchodilatory effects of beta-agonists 2
• Be cautious with medications that may affect glucose levels or electrolytes in patients with respiratory infections 2

Special Considerations

• For patients with suspected influenza, consider initiating antiviral treatment within 48 hours of symptom onset 1
• In immunocompromised patients, consider broader differential diagnoses including opportunistic infections 1
• For patients on corticosteroids or other immunosuppressants, consider Pneumocystis jirovecii pneumonia, particularly with high respiratory rates or oxygen desaturation 1
• Be alert for immune-related adverse events in patients treated with immune checkpoint inhibitors 1

Pitfalls to Avoid

• Do not rely solely on clinical presentation for diagnosis of pneumonia, as this approach is overly sensitive 1
• Avoid unnecessary antibiotic use for viral respiratory infections 3, 4
• Do not delay obtaining respiratory specimens before initiating or changing antibiotics 1
• Remember that tracheal colonization is common in intubated patients but does not necessarily indicate infection requiring treatment 1
• Be aware that purulent tracheobronchitis may mimic many clinical signs of pneumonia and may require different management 1

By systematically addressing these considerations in the workup of a patient with suspected respiratory infection, clinicians can ensure appropriate diagnosis and management while avoiding unnecessary testing and treatments.