Pneumonia laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. ;Associate Editor(s)-in-Chief: Hamid Qazi, MD, BSc , Alejandro Lemor, M.D. 
Laboratory findings such as leukocytosis are helpful for the diagnosis of bacterial pneumonia or to assess the status of the patient. Sputum samples need to be collected from every patient and gram staining and culture need to be performed to determine the exact pathogen causing the pneumonia. Other tests include urine antigen test, PCR, C-reactive protein, and procalcitonin.
|Urinary Antigen Test for Pneumococcus|
|Urinary Antigen Test for Legionella|
|Adapted from IDSA/ATS Guidelines for CAP in Adults|
Findings in routine blood tests are based on the severity of the disease and the cause, they can include the following:
- Leukocytosis with left shift (in cases of bacterial pneumonia)
- Leukopenia (in cases of atypical pneumonia)
- Eosinophilia (in cases of eosinophilic pneumonia)
- Elevated BUN
- Findings of lactic acidosis (decreased HCO3, increased lactic acid levels)
- ABG: may show hypoxia and/or hypercapnea
Sputum Gram Stain and Culture
- Sputum samples should be obtained of all patients with productive cough.
- Gram-stain and culture should be performed to assess the causative agent and guide the therapy.
- In more than 80% of cases of pneumococcal pneumonia the sputum culture is positive.
- Blood cultures should be obtained for patients with severe disease, patients that require hospitalization, and patients in which antibiotic therapy failed.
- Blood culture may be positive in cases of hematogenous spread, such as S. aureus pneumonia, and in around one fourth of patients with pneumococcal pneumonia.
Other Laboratory Tests
Urine Antigen Test 
- Usually used to diagnose Legionella disease.
- Useful also in the diagnosis of pneumonia caused by Streptococcus pneumoniae, with a sensitivity of 74.6% and an association with worst clinical outcome.
- The presence of the antigen in urine can be detected in 24 hours since the onset of the symptoms.
- The severity of Legionella disease increases the sensitivity of the urinary antigen test.
- Urinary antigen test is not recommended in the diagnosis of pneumococcal pneumonia in children due to the high rate of false-positive results.
Polymerase Chain Reaction
- Polymerase chain reaction (PCR) is more useful in the diagnosis of viral and mycoplasma pneumonia.
- C-reactive protein (CRP) may be helpful to differentiate between bacterial from viral pneumonia.
- It has been reported that CRP is elevated (> 100 mg/L) in cases of bacterial pneumonia.
- Procalcitonin levels are associated with the severity of the pneumonia and the etiology.
- This biomarker also helps to differentiate between bacterial and non-bacterial disease.
Community Acquired Pneumonia
The infectious diseases society of America/American thoracic society consensus recommendation on diagnostics test for etiology of community-acquired pneumonia in adults are as follows:
Recommended Diagnostic Tests for Etiology
For Level of evidence and classes click here.
Hospital Acquired Pneumonia
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)
- 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 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.
- Specific blood serology tests for other bacteria (Mycoplasma, Legionella and Chlamydophila) can be done in conditions with strong suspicion of the causative organisms.
Respiratory Samples for VAP
- Tracheo-bronchial aspiration
- Mini-bronchoalveloar lavage
- Tracheobronchial aspiration - > 1 million cfu / mL is
- Bronchoalveolar lavage - > 10,000 cfu / mL
- PSB (protected brush sampling) - > 1,000 cfu / mL
- 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.
- 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 
For Level of evidence and classes click here.
- ↑ Mandell, L. A.; Wunderink, R. G.; Anzueto, A.; Bartlett, J. G.; Campbell, G. D.; Dean, N. C.; Dowell, S. F.; File, T. M.; Musher, D. M.; Niederman, M. S.; Torres, A.; Whitney, C. G. (2007). "Infectious Diseases Society of America/American Thoracic Society Consensus Guidelines on the Management of Community-Acquired Pneumonia in Adults". Clinical Infectious Diseases. 44 (Supplement 2): S27–S72. doi:10.1086/511159. ISSN 1058-4838.
- ↑ Solomon, Caren G.; Wunderink, Richard G.; Waterer, Grant W. (2014). "Community-Acquired Pneumonia". New England Journal of Medicine. 370 (6): 543–551. doi:10.1056/NEJMcp1214869. ISSN 0028-4793.
- ↑ Musher, Daniel M.; Thorner, Anna R. (2014). "Community-Acquired Pneumonia". New England Journal of Medicine. 371 (17): 1619–1628. doi:10.1056/NEJMra1312885. ISSN 0028-4793.
- ↑ Couturier MR, Graf EH, Griffin AT (2014). "Urine antigen tests for the diagnosis of respiratory infections: legionellosis, histoplasmosis, pneumococcal pneumonia". Clin Lab Med. 34 (2): 219–36. doi:10.1016/j.cll.2014.02.002. PMID 24856525.
- ↑ Zalacain R, Capelastegui A, Ruiz LA, Bilbao A, Gomez A, Uranga A; et al. (2014). "Streptococcus pneumoniae antigen in urine: diagnostic usefulness and impact on outcome of bacteraemic pneumococcal pneumonia in a large series of adult patients". Respirology. 19 (6): 936–43. doi:10.1111/resp.12341. PMID 24976113.
- ↑ Bradley JS, Byington CL, Shah SS, Alverson B, Carter ER, Harrison C; et al. (2011). "The management of community-acquired pneumonia in infants and children older than 3 months of age: clinical practice guidelines by the Pediatric Infectious Diseases Society and the Infectious Diseases Society of America". Clin Infect Dis. 53 (7): e25–76. doi:10.1093/cid/cir531. PMID 21880587.
- ↑ Flanders, Scott A; Stein, John; Shochat, Guy; Sellers, Karen; Holland, Miles; Maselli, Judith; Drew, W.Lawrence; Reingold, Art L; Gonzales, Ralph (2004). "Performance of a bedside c-reactive protein test in the diagnosis of community-acquired pneumonia in adults with acute cough". The American Journal of Medicine. 116 (8): 529–535. doi:10.1016/j.amjmed.2003.11.023. ISSN 0002-9343.
- ↑ Johansson, Niclas; Kalin, Mats; Backman-Johansson, Carolina; Larsson, Anders; Nilsson, Kristina; Hedlund, Jonas (2014). "Procalcitonin levels in community-acquired pneumonia – correlation with aetiology and severity". Scandinavian Journal of Infectious Diseases. 46 (11): 787–791. doi:10.3109/00365548.2014.945955. ISSN 0036-5548.
- ↑ Mandell LA, Wunderink RG, Anzueto A, Bartlett JG, Campbell GD, Dean NC, Dowell SF, File TM, Musher DM, Niederman MS, Torres A, Whitney CG (2007). "Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults". Clinical Infectious Diseases : an Official Publication of the Infectious Diseases Society of America. 44 Suppl 2: S27–72. doi:10.1086/511159. PMID 17278083. Retrieved 2012-09-06. Unknown parameter
- ↑ "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