If pneumonia is suspected on the basis of a patient's symptoms and findings from physical examination, further investigations are needed to confirm the diagnosis. Information from a chest X-ray and blood tests are helpful, and sputum cultures in some cases. The chest X-ray is typically used for diagnosis in hospitals and some clinics with X-ray facilities. However, in a community setting (general practice), pneumonia is usually diagnosed based on symptoms and physical examination alone. Diagnosing pneumonia can be difficult in some people, especially those who have other illnesses. Occasionally a chest CT scan or other tests may be needed to distinguish pneumonia from other illnesses.
An important test for pneumonia in unclear situations is a chest x-ray. Chest x-rays can reveal areas of opacity (seen as white) which represent consolidation. Pneumonia is not always seen on x-rays, either because the disease is only in its initial stages, or because it involves a part of the lung not easily seen by x-ray. In some cases, chest CT (computed tomography) can reveal pneumonia that is not seen on chest x-ray. X-rays can be misleading, because other problems, like lung scarring and congestive heart failure, can mimic pneumonia on x-ray. Chest x-rays are also used to evaluate for complications of pneumonia (''see below.'')
If antibiotics fail to improve the patient's health, or if the health care provider has concerns about the diagnosis, a culture of the person's sputum may be requested. 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 blood sample may similarly be cultured to look for bacteria in the blood. Any bacteria identified are then tested to see which antibiotics will be most effective.
A complete blood count may show a high white blood cell count, indicating the presence of an infection or inflammation. In some people with immune system problems, the white blood cell count may appear deceptively normal. Blood tests may be used to evaluate kidney function (important when prescribing certain antibiotics) or to look for low blood sodium. Low blood sodium in pneumonia is thought to be due to extra anti-diuretic hormone produced when the lungs are diseased (SIADH). Specific blood serology tests for other bacteria (''Mycoplasma'', ''Legionella'' and ''Chlamydophila'') and a urine test for ''Legionella'' antigen are available. Respiratory secretions can also be tested for the presence of viruses such as influenza, respiratory syncytial virus, and adenovirus. Liver function tests should be carried out to test for damage caused by sepsis.
- Temperature > 100 degrees F (37.8 degrees C)
- Pulse > 100 beats/min
- Decreased breath sounds
- ''Absence'' of asthma
The probability of an infiltrate in two separate validations was based on the number of findings:
- 5 findings - 84% to 91% probability
- 4 findings - 58% to 85%
- 3 findings - 35% to 51%
- 2 findings - 14% to 24%
- 1 findings - 5% to 9%
- 0 findings - 2% to 3%
A subsequent study comparing four prediction rules to physician judgment found that two rules, the one above were more accurate than physician judgment because of the increased specificity of the prediction rules.
Several diseases and/or conditions can present with similar clinical features to pneumonia and as such care must be taken in the proper diagnosis of the disease. Chronic obstructive pulmonary disease (COPD) or asthma can present with a polyphonic wheeze, similar to that of pneumonia. Pulmonary edema can be mistaken for pneumonia due to its ability to show a third heart sound and present with an abnormal ECG. Other diseases to be taken into consideration include bronchiectasis, lung cancer and pulmonary emboli.
A vaccine against ''Streptococcus pneumoniae'' is also available for adults. In the U.S., it is currently recommended for all healthy individuals older than 65 and any adults with emphysema, congestive heart failure, diabetes mellitus, cirrhosis of the liver, alcoholism, cerebrospinal fluid leaks, or those who do not have a spleen. A repeat vaccination may also be required after five or ten years.
Influenza vaccines should be given yearly to the same individuals who receive vaccination against ''Streptococcus pneumoniae''. In addition, health care workers, nursing home residents, and pregnant women should receive the vaccine. When an influenza outbreak is occurring, medications such as amantadine, rimantadine, zanamivir, and oseltamivir can help prevent influenza.
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