Pneumonia - Hospital-Acquired Diagnostics

Cultures  

Cultures should be collected before antibiotics are started or changed. Blood samples should be taken from two separate sites. If blood cultures isolate a pathogen, other sites of infection will need to be excluded. Other samples used for culture include sputum, pleural fluid, and endotracheal or transtracheal aspirate.

Endotracheal Aspiration  

Endotracheal aspiration is a non-invasive sampling technique preferred over invasive techniques, together with semiquantitative cultures to confirm ventilator-associated pneumonia. Distal quantitative samples are preferred over proximal samples for VAP patients.  

Invasive Microbiologic Techniques  

Invasive microbiologic techniques include bronchoalveolar lavage (BAL), protected specimen brushing, and blind bronchial sampling. The etiologic pathogen is determined if a specimen contains organism(s) above a predetermined threshold concentration.  

Arterial Blood Gas or Oximetry  

Arterial blood gas or oximetry is generally measured in all patients to determine the severity of illness and the need for supplemental oxygen (O₂) or mechanical ventilation.







SARS-CoV-2 Polymerase Chain Reaction Assay  

SARS-CoV-2 polymerase chain reaction assay of the nasopharyngeal aspirate, nose and throat swabs, or lower respiratory tract samples (endotracheal aspirate, BAL) may help identify patients with coronavirus disease 2019 (COVID-19) infection.







Multiplex Polymerase Chain Reaction (mPCR) Tests  

Example tests: Unyvero HPN (Curetis, UnyveroTM), FilmArray Pneumonia+ Panel (BioFire, bioMérieux)  

Multiplex polymerase chain reaction (mPCR) tests provide a rapid and sensitive approach for diagnosing hospital-acquired pneumonia through simultaneous detection of multiple pathogens from respiratory samples (eg sputum, endotracheal aspirate, BAL). These enhance and guide antimicrobial therapy by identifying pathogens and their antibiotic resistance, thereby allowing timely and targeted antibiotic treatment. These offer valuable diagnostic information but should not be used alone or replace traditional culture methods, which can provide additional information about antibiotic susceptibility.  

Other Laboratory Tests  

Other laboratory tests include complete blood count (CBC), serum electrolytes, renal and liver function, and serum biomarkers (eg CRP, procalcitonin [PCT], copeptin, mid-regional pro-atrial natriuretic peptide [MR-proANP]). CRP and PCT are inflammatory biomarkers that can help assess severity and guide treatment. These are not useful for determining the etiologic organism and should be interpreted in conjunction with other clinical and laboratory findings. These may be useful to document the presence of organ dysfunction to assist in determining the severity of illness.

Chest X-ray    

Both posterior-anterior and lateral views in chest x-ray are recommended. Chest x-ray helps to identify disease severity and the presence of complications (eg effusion, cavitation).  

Clinical Evidence that New or Progressive Infiltrate is Consistent with Pneumonia

At least two of the following clinical evidence should be present:

• Fever >38°C
• Purulent sputum
• Leukocytosis (white blood cells [WBC] >12,000 cells/mm³ [12x10⁹ cells/L]) or leukopenia (WBC <4,000 cells/mm³ [4x10⁹cells/L])

There is high sensitivity even if only one criterion is used, but low specificity is noted for VAP.