Diagnostic Difficulties in Community-Acquired Pneumonia (CAP). It is important to determine whether the cause of CAP is a bacterium, atypical bacterium, or virus, because they require different treatments. In children, for example, S. pneumoniae is the most common cause of pneumonia, but respiratory syncytial virus may also cause the disease. Although symptoms may differ, they often overlap, which can make it difficult to identify the organism by symptoms alone. The cause of CAP is found in only about half of cases.
Nevertheless, in many cases of mild-to-moderate CAP, the physician is able to diagnose and treat pneumonia based solely on a medical history and physical examination.
Diagnostic Difficulties with Hospital-Acquired (Nosocomial) Pneumonia. Diagnosing pneumonia is particularly difficult in hospitalized patients for a number of reasons:
The patient's history is an important part of making a pneumonia diagnosis. Patients should be sure to report any of the following:
Use of the Stethoscope. The most important diagnostic tool for pneumonia is the stethoscope. Sounds in the chest that may indicate pneumonia include:
Although current antibiotics can destroy a wide spectrum of organisms, it is best to use an antibiotic that targets the specific one making a person sick. Unfortunately, people carry many bacteria, and sputum and blood tests are not always effective in distinguishing between harmless and harmful kinds.
In severe cases, a doctor needs to use invasive diagnostic measures to identify the cause of the infection. Standard lab tests used to help diagnose pneumonia include:
Sputum Tests. The color of the mucus (sputum) sample coughed up from the lungs can reveal the severity of the disease. Only a sputum sample will reveal the organism causing the infection.
The patient coughs as deeply as possible to bring up mucus from the lungs, since a shallow cough produces a sample that usually only contains normal mouth bacteria. Some people may need to inhale a saline spray to produce an adequate sample. In some cases, a tube will be inserted through the nose into the lower respiratory tract to trigger a deeper cough.
The physician will check the sputum for:
The sputum sample is sent to the laboratory, where it is analyzed for the presence of bacteria and to determine whether the bacteria are Gram-negative or Gram-positive.
Blood Tests. The following blood tests may be performed:
Urine Tests. Urine antigen tests for Legionella pneumophila (Legionnaires' disease) and Streptococcus pneumoniae may be performed in patients with severe CAP. The S. pneumoniae test takes only 15 minutes and may identify up to 77% of pneumonia cases and rule out S. pneumoniae infection in 98% of patients. It may not be useful in children.
Invasive Tests. In critically-ill patients with ventilator-associated pneumonia, doctors have tried sampling fluid taken from the lungs or trachea. These techniques enabled the physicians to identify the pneumonia-causing bacteria and start the appropriate antibiotics. However, this made no difference in the length of stay in the ICU or hospital, and there was no significant difference in outcome.
X-Rays. A chest x-ray is nearly always taken to confirm a pneumonia diagnosis.
A chest x-ray may reveal the following:
Other Imaging Tests. Computed tomography (CT) scans or magnetic resonance imaging (MRI) scans may be useful in some circumstances, especially when:
CT and MRI can help detect tissue damage, abscesses, and enlarged lymph nodes. They can also detect some tumors that block bronchial tubes. No imaging technique can determine the actual organism causing the infection. However, features on the CT scan of patients with certain forms of pneumonia -- for example, that caused by Legionella pneumophila -- are usually different from features produced by other bacteria in the lungs.
Invasive diagnostic procedures may be required when:
Invasive procedures include:
Thoracentesis. If a doctor detects pleural effusion during the physical exam or on an imaging study, and suspects that pus (empyema) is present, a thoracentesis is performed.
Complications of this procedure are rare, but can include collapsed lung, bleeding, and infection.
Bronchoscopy. Bronchoscopy is an invasive test to examine respiratory secretions. It is not usually needed in patients with community-acquired pneumonia, but it may be appropriate for patients with a severely compromised immune system who need immediate diagnosis, or in patients whose condition has worsened during treatment.
A bronchoscopy is done in the following way:
Bronchoalveolar lavage (BAL) may be done at the same time as bronchoscopy. This involves injecting high amounts of saline through the bronchoscope into the lung and then immediately sucking the fluid out. The fluid is then analyzed in the laboratory. Studies find BAL to be an effective method for detecting specific infection-causing organisms.
The procedure is usually very safe, but complications can occur. They include:
Lung Biopsy. In very severe cases of pneumonia or when the diagnosis is unclear, particularly in patients with a damaged immune system, a lung biopsy may be required. A lung biopsy involves taking some tissue from the lungs and examining it under a microscope.
Lung Tap. This procedure typically uses a needle inserted between the ribs to draw fluid out of the lung for analysis. It is known by a number of names, including:
It is a very old procedure that is not done often any more, because it is invasive and poses a slight risk for collapsed lung. Some experts argue, however, that a lung tap is more accurate than other methods for identifying bacteria, and the risk it poses is slight. Given the increase in resistant bacteria, they believe its use should be reconsidered in young people.
Common Causes of Persistent Coughing. Persistent coughing is nearly always temporary and harmless when other symptoms, such as fever, are not present. The four most common causes of persistent coughing are:
Other common causes of chronic cough include heavy smoking or the use of heart drugs known as ACE inhibitors.
Acute Bronchitis. Acute bronchitis is an infection in the passages that carry air from the throat to the lung. The infection causes a cough that produces phlegm. Acute bronchitis is almost always caused by a virus and usually clears up on its own within a few days. In some cases, acute bronchitis caused by a cold can last for several weeks.
Chronic Bronchitis. Chronic bronchitis causes shortness of breath and is often accompanied by infection, mucus production, and coughing, but it is a long-term and irreversible condition. The same bacteria and viruses that cause pneumonia can cause an infection in patients with chronic bronchitis. However, infections involve only the airways leading to the lungs, and not the lung tissue itself. The two disorders may share the same symptoms, such as:
There are significant differences between chronic bronchitis and pneumonia:
Asthma. In asthma, the cough is accompanied by wheezing and occurs mostly at night or during activity. Fever is rarely present (unless the patient also has an infection). Asthma symptoms from occupational causes can lead to persistent coughing, which is usually worse during the work week. Tests -- the methacholine inhalation challenge and pulmonary function studies -- may be effective in diagnosing asthma.
Other Disorders that Affect the Lung. Many conditions mimic pneumonia, particularly in hospitalized patients. They include:
Ruling Out Causes in Children. Important causes of coughing in children at different ages include:
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