Hospital-acquired pneumonia laboratory findings

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Editor(s)-in-Chief: C. Michael Gibson, M.S., M.D. ; Philip Marcus, M.D., M.P.H.; Associate Editor(s)-in-Chief: Alejandro Lemor, M.D. [1]


Current guidelines recommend a combination of chest X-ray, laboratory data as well as clinical judgment in diagnosis and management of community acquired pneumonia. Laboratory tests include CBC, metabolic panel, sputum gram-stain and culture, serology for mycoplasma, chlamydia, and legionella. Additional test include bronchial samples and HIV testing for special conditions.

Laboratory Findings

Basic Blood Works


Sputum Culture

  • Sputum gram stain and culture have poor yield. Sputum culture provides diagnostics information in roughly 1 in 5 patients only.
  • Sputum cultures generally take at least two to three days, so they are mainly used to confirm that the infection is sensitive to an antibiotic that has already been started.
  • A good sputum sample contains small number of squamous epithelial cells and a large number of PMNs.

Blood Culture

  • Blood cultures are not recommended for the outpatient management of CAP due to the low yield of pathogens.
  • A blood sample may similarly be cultured to look for infection in the blood (blood culture). Any bacteria identified are then tested to see which antibiotics will be most effective.


Oxygen Monitoring

Respiratory Samples for VAP

Bronchial Samples Over Non-bronchial Sample
Advantages Disadvantages
  • Helps in accurate diagnosis and selection of narrow antibiotic regimen. Thus, decreases incidence of antibiotic resistance.
  • Quantitative cultures from nonbronchoscopic specimens have a lower specificity than quantitative cultures derived from bronchoscopic specimens.
  • Obtaining bronchial sample is more invasive and risk of injuries are more compared to the non-invasive methods.

Bronchial Samples

Non-Bronchial Sample

  • Tracheo-bronchial aspiration
  • Mini-bronchoalveloar lavage

Quantitative Culture

  • Tracheobronchial aspiration - > 1 million cfu / mL is
  • Bronchoalveolar lavage - > 10,000 cfu / mL
  • PSB (protected brush sampling) - > 1,000 cfu / mL

Semi-quantitative Culture

  • Report bacterial growth as heavy, moderate, light, or no growth.
  • A moderate to heavy growth is suggestive of ventilator associated pneumonia.
  • More false positive results compared to quantitative cultures.

Special Tests

  • In more severe cases, (bronchoscopy) can be used collect fluid for culture.
  • Special tests can be performed if an uncommon microorganism is suspected (such as testing the urine for Legionella antigen when Legionnaires' disease is a concern).
  • HIV testing should be performed on all patients presenting with CAP (ages 13 to 75) in a medical setting.
  • Respiratory secretions can also be tested for the presence of viruses such as influenza, respiratory syncytial virus, and adenovirus.

Major Points and Recommendations for Laboratory Tests in Adults with Hospital-Acquired, Ventilator-Associated, and Healthcare-Associated Pneumonia [1]

  • All patients with suspected VAP should have blood cultures collected, recognizing that a positive result can indicate the presence of either pneumonia or extrapulmonary infection (Level II).
  • A diagnostic thoracentesis to rule out a complicating empyema or parapneumonic effusion should be performed if the patient has a large pleural effusion or if the patient with a pleural effusion appears toxic (Level III).
  • Samples of lower respiratory tract secretions should be obtained from all patients with suspected HAP, and should be collected before antibiotic changes. Samples can include an endotracheal aspirate, bronchoalveolar lavage sample, or protected specimen brush sample (Level II)

For Level of evidence and classes click here.


  1. "Guidelines for the management of adults with hospital-acquired, ventilator-associated, and healthcare-associated pneumonia". American Journal of Respiratory and Critical Care Medicine. 171 (4): 388–416. 2005. doi:10.1164/rccm.200405-644ST. PMID 15699079. Retrieved 2012-09-13. Unknown parameter |month= ignored (help)

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