Hospital-acquired pneumonia laboratory findings

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Editor(s)-in-Chief: C. Michael Gibson, M.S., M.D. [1] Phone:617-632-7753; Philip Marcus, M.D., M.P.H.[2]

Overview

Current guidelines recommend a combination of chest Xray,laboratory data as well as clinical judgment in diagnosis and management of community acquired pneumonia.

Infectious Diseases Society of America/American Thoracic Society consensus recommendation on diagnostics test for etiology of community-acquired pneumonia in adults. (DONOT EDIT)

“

Recommended Diagnostic Tests for Etiology Patients with CAP should be investigated for specific pathogens that would significantly alter standard (empirical) management decisions, when the presence of such pathogens is suspected on the basis of clinical and epidemiologic clues. (Strong recommendation; level II evidence) Routine diagnostic tests to identify an etiologic diagnosis are optional for outpatients with CAP. (Moderate recommendation; level III evidence) Pretreatment blood samples for culture and an expectorated sputum sample for stain and culture (in patients with a productive cough) should be obtained from hospitalized patients with the clinical indications, but are optional for patients without these conditions. (Moderate recommendation; level I evidence) Pretreatment Gram stain and culture of expectorated sputum should be performed only if a good-quality specimen can be obtained and quality performance measures for collection, transport, and processing of samples can be met. (Moderate recommendation; level II evidence) Patients with severe CAP, as defined in the guideline should at least have blood samples drawn for culture, urinary antigen tests for Legionella pneumophila and Streptococcus pneumoniae performed, and expectorated sputum samples collected for culture. For intubated patients, an endotracheal aspirate sample should be obtained. (Moderate recommendation; level II evidence)

”

For Level of evidence and classes click here.

Lab diagnosis

Basic blood works

• Complete blood count (leucocytosis). In some people with compromised immunity, the white blood cell count may appear deceptively normal.
• Basic metabolic panel
  • Used to evaluate kidney function when prescribing certain antibiotics
  • Hyponatremia in pneumonia is thought to be due to excess anti-diuretic hormone produced when the lungs are diseased (SIADH)

Culture

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.

Serology

• Specific blood serology tests for other bacteria (Mycoplasma, Legionella and Chlamydophila) can be done in conditions with strong suspicion of the causative organisms.

Oxygen monitoring

• Pulse oximeter
• Arterial blood gas

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.