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Sputum, Investigation

Microbiological screening of sputum is used to investigate lower respiratory tract infections, including pneumonia.

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Common microbial agents of acute pneumonia include Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae, Pseudomonas aeruginosa as well as various members of the Enterobacteriaceae (Escherichia coli, Enterobacter) family. Usually, individual history, physical examination and plain chest x-rays are sufficient to diagnose pneumonia and initiate appropriate antimicrobial therapy.

Both the sensitivity and specificity of sputum cultures are generally considered to be low (<50%). Crop specialty can be improved by appropriately collecting sputum from the lower respiratory tract and avoiding oral and pharyngeal contamination.

Specific microbiological screening of sputum does not detect certain pathogens that cause lower respiratory tract infections and require special procedures. Uncontrolled microorganisms are:

  • Mycobacteria (Mycobacerium sp.)
  • Legionella sp.
  • Pneumonia mycoplasma (Mycoplasma pneumoniae)
  • Pneumocystis (Pneumocystis jiroveci)



Pneumonia can be classified according to whether it is outpatient or inpatient (defined as pneumonia occurring 48 or more hours after hospital admission). It can be primary when it occurs to a person without any risk factors or secondary. Many conditions are associated with an increased risk of pneumonia. Common risk factors include chronic lung diseases such as chronic obstructive pulmonary disease (COPD), diabetes mellitus, heart or kidney failure and immunosuppression (congenital or acquired). Decreased level of consciousness and inability to reflect cough are risk factors for aspiration pneumonia. Recent infections of the respiratory tract with viruses, especially influenza, are also a risk factor. There are some clinical points and laboratory markers that can be used to assess the severity of pneumonia.

The etiology of pneumonia varies depending on whether it has been acquired in the community or hospital and also the presence of certain risk factors. Many of the germs found as colonizers in the upper respiratory tract have been implicated as causes of pneumonia. Previous antibiotic treatment and hospitalization have affected flora, leading to an increase in the number of aerobic Gram-negative microbes. These factors influence the sensitivity and specificity of sputum culture as a diagnostic test and the results should always be interpreted in the light of clinical information.




Important Note

Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. Correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".

Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.

At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.

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