From the Guidelines
Blood work for pneumonia should include a complete blood count (CBC) with differential leukocyte count and platelet count, as well as blood cultures to identify the specific bacteria causing the infection, as recommended by the Infectious Diseases Society of America 1.
Key Components of Blood Work for Pneumonia
- A CBC count with differential leukocyte count and platelet count to check for elevated white blood cells, which indicate infection
- Blood cultures to identify the specific bacteria causing the infection, with at least 2 sets of blood cultures recommended, collected simultaneously from each lumen of an existing central venous catheter (CVC) and from a peripheral vein site 1
- Measurement of serum levels of creatinine and blood urea nitrogen, as well as electrolytes, hepatic transaminase enzymes, and total bilirubin 1
Additional Tests
- C-reactive protein (CRP) and procalcitonin to assess inflammation severity
- Comprehensive metabolic panel to evaluate organ function
- Arterial blood gases to measure oxygen levels in severe cases
- Sputum cultures, respiratory viral panels, and urinary antigen tests for specific pathogens like Streptococcus pneumoniae and Legionella may be ordered for hospitalized patients
Importance of Timely Blood Work
- Blood cultures should be collected prior to antibiotic therapy in patients hospitalized for pneumonia, as recommended by the Clinical Infectious Diseases guidelines 1
- Antibiotic therapy should be initiated within 4 hours after registration for hospitalized patients with community-acquired pneumonia (CAP) 1
Monitoring Treatment Response
- Blood work results typically show leukocytosis (elevated white blood cells), often with a left shift (increased immature neutrophils), and elevated inflammatory markers, which help clinicians monitor treatment response and adjust therapy as needed
- Regular assessment of oxygenation by arterial blood-gas testing or pulse oximetry is also crucial in severe cases 1
From the Research
Blood Work for Pneumonia
- Blood cultures are of limited utility in nonsevere community-acquired pneumonia, though routinely recommended for severe community-acquired pneumonia or health care-associated pneumonia due to perceived greater bacteremia risk, particularly with multidrug-resistant organisms 2.
- The yield of blood cultures in patients with pneumonia is low, with only 6.6% of patients having bacteremia, and a greater incidence in severe community-acquired pneumonia (14.7%) than nonsevere community-acquired pneumonia (7.8%) and health care-associated pneumonia (6.6%) 2.
- Predictive factors of true bacteremia in patients with community-onset pneumonia include chronic liver disease, a confusion, urea, respiratory rate, blood pressure, age ≥65 (CURB-65) score of 4 to 5 points, and Pneumonia Severity Index (PSI) class V 3.
- Bacteremia in pneumococcal pneumonia is of prognostic significance, with patients having a greater likelihood of septic shock, in-hospital mortality, 15-day mortality, and 30-day mortality compared to those without bacteremia 4.
- In children hospitalized with community-acquired pneumonia, the yield of blood cultures is low, and predictors of bacteremia include a white blood cell count >20 × 10^3 cells per µL and definite radiographic pneumonia, but the prevalence of penicillin-nonsusceptible bacteremia is below 1% even in the presence of individual predictors 5.
- Procalcitonin (PCT) is a reliable diagnostic and prognostic biomarker of infection or sepsis in patients presenting to the emergency department, and its combination with white blood cell (WBC) count and C reactive protein (CRP) can guide antibiotic therapy 6.