Indications for Testing
Laboratory testing for HAP/VAP is appropriate in the following circumstances:
- Diagnosis in hospitalized patients or patients receiving mechanical ventilation with new-onset fever, purulent sputum, leukocytosis, and/or decline in oxygenation
- Monitoring to guide treatment decisions in patients diagnosed with HAP/VAP (See Monitoring below)
Criteria for Diagnosis
|Presence of infiltrate, plus clinical evidence of infectious origin of infiltrate (new onset of fever, purulent sputum, leukocytosis, decline in oxygenation)
||Pneumonia occurring >48 hrs after admission (not due to progression of disease present at admission)a; not associated with mechanical ventilation
||Pneumonia occurring >48 hrs after endotracheal intubation
|aClinical criteria are recommended for diagnosis of HAP/VAP, as opposed to clinical criteria in conjunction with serum procalcitonin, sTREM-1, CRP, or Clinical Pulmonary Infection Score.
CRP, C-reactive protein; sTREM-1, soluble triggering receptor expressed on myeloid cells
Sources: Infectious Diseases Society of America (IDSA)/American Thoracic Society (ATS), 2016
CBC is a useful initial test for HAP/VAP and is best performed near the point of care. Patients with HAP/VAP may demonstrate leukocytosis. Arterial blood gas testing or oximetry is also indicated.
Gram Stain and Culture
Culture of respiratory secretions is a primary test for HAP/VAP diagnosis and is also best performed near the point of care. Guidelines recommend a noninvasive collection method such as endotracheal aspiration and semiquantitative rather than quantitative culture for patients with suspected VAP. Invasive methods such as bronchoalveolar lavage (BAL), protected specimen brush (PSB), and blind bronchial sampling are discouraged due to increased risk.
Noninvasive collection is also recommended in patients with suspected HAP, when possible. It may be necessary to induce sputum, and nasotracheal suction or endotracheal aspiration may be required if the patient is unable to produce sputum or was recently placed on mechanical ventilation.
Blood cultures are minimally invasive and inexpensive, low risk, and can detect sepsis. Data to support the use of blood cultures in patients with suspected HAP/VAP are limited. However, in some patients with bacteremic illness, the identification of a particular pathogen may guide clinical decision making; therefore, current guidelines still recommend blood cultures be obtained in cases of suspected HAP and VAP.
Some additional tests have been proposed for HAP/VAP diagnosis, but current data are insufficient to support their use. Tests for procalcitonin (PCT) concentration and sTREM-1 are still being studied to evaluate their role in diagnosis. Some reports suggest that CRP testing may help to determine whether to begin antibiotic treatment. However, none of these tests are recommended in the current guidelines.
The role of multiplex molecular tests, such as PCR panels (also called syndromic panels) and NGS, is yet to be determined. As such, they are not yet recommended in guidelines for HAP/VAP testing. These tests show promise in their ability to identify a range of pathogens and potentially help guide treatment decisions. However, targeted PCR-based tests are generally more sensitive and are preferred when specific pathogens are suspected.
PCT concentrations, although not recommended for diagnosis, can be useful in combination with clinical criteria to guide discontinuation of antibiotic treatment in patients with HAP/VAP.