From the Guidelines
Pneumonia can be confirmed by several laboratory tests, including chest radiography, complete blood cell and differential counts, serum creatinine, urea nitrogen, glucose, electrolyte, bilirubin, and liver enzyme values, as well as blood cultures and Gram stain and culture of sputum 1.
Diagnostic Tests for Pneumonia
- Chest radiography is required for the routine evaluation of patients who are likely to have pneumonia, to establish the diagnosis and to aid in differentiating CAP from other common causes of cough and fever, such as acute bronchitis 1.
- Blood cultures can help identify the causative agent of pneumonia, particularly in high-risk community-acquired pneumonia patients 1.
- Sputum Gram stain and culture can help identify the causative agent of pneumonia, but the specimen should be collected before antibiotic therapy and interpreted by trained personnel 1.
- Complete blood cell and differential counts can help assess the severity of pneumonia and identify potential complications 1.
- Serum tests, such as serum creatinine, urea nitrogen, glucose, electrolyte, bilirubin, and liver enzyme values, can help assess the patient's overall health and identify potential complications 1.
Special Considerations
- Immunocompromised patients may require a broader diagnostic approach, including invasively obtained specimens 1.
- Patients with severe pneumonia or clinical features that suggest legionnaires’ disease should undergo culture and urinary antigen testing for Legionella 1.
- Patients with cough for ≥2 weeks, other common symptoms, or suggestive radiographic changes should be tested for Mycobacterium tuberculosis 1.
From the Research
Laboratory Diagnosis of Pneumonia
The diagnosis of pneumonia can be confirmed through various laboratory tests, including:
- Gram's stain and culture of the sputum, which are still the most useful techniques for the diagnosis of bacterial pneumonia 2
- Antigen detection, which can provide a rapid diagnosis and contribute to the initial choice of therapy in infections caused by certain microorganisms, such as Haemophilus influenzae, Legionella pneumophila, Chlamydia psittaci, and Pneumocystis carinii 2
- Blood cultures, serological tests, and fibreoptic bronchoscopy, which can be used to diagnose pneumonia, especially in hospitalized patients 3
Diagnostic Techniques
Different diagnostic techniques have their own advantages and disadvantages, including:
- Sputum culture, which can be contaminated with oropharyngeal commensal flora and may not always yield positive results 3
- Blood cultures, which can be used to diagnose bacteremia, but may not always be positive in patients with pneumonia 3
- Serological tests, which can be used to diagnose certain types of pneumonia, such as Mycoplasma pneumoniae, but may not always be positive in patients with pneumonia 3
- Fibreoptic bronchoscopy, which can be used to diagnose pneumonia, especially in ventilator-associated pneumonia, but may not always be necessary 3
Biomarkers
Certain biomarkers, such as C-reactive protein (CRP) and procalcitonin (PCT), can be used to diagnose pneumonia and monitor the response to treatment, including:
- CRP, which can be elevated in patients with pneumonia and can be used to diagnose and monitor the response to treatment 4, 5
- PCT, which can be elevated in patients with bacterial pneumonia and can be used to diagnose and monitor the response to treatment 5
Molecular Diagnostics
Molecular diagnostics, such as pneumococcal PCR, can be used to diagnose pneumonia and identify the causative microorganism, including:
- Pneumococcal PCR, which can be used to diagnose pneumococcal pneumonia and monitor the response to treatment 5