Diagnosis

Diagnostic Difficulties in Community-Acquired Pneumonia (CAP). It is important to determine if the cause of CAP is bacteria, atypical bacteria, or a virus, since they all require different treatments. In children, for example, S. pneumonia is the most common cause, 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.

Nevertheless, in many cases of mild-to-moderate community-acquired pneumonia, the physician is able to diagnose and treat pneumonia based solely on a history and physical examination.

Diagnostic Difficulties in Hospital-Acquired (Nosocomial) Pneumonia. Diagnosing pneumonia is particularly difficult in hospitalized patients for a number of reasons:

• Many hospitalized patients have similar symptoms, including fever or signs of lung infiltration on x-rays.
• In hospitalized patients, sputum or blood tests often indicate the presence of bacteria or other organisms, but such agents do not necessarily indicate pneumonia.

Doctors making a diagnosis of pneumonia should rule out other conditions, using a chest x-ray, two sets of blood cultures, a urine analysis for Legionella, and a lung fluid sample, among other tests.

Medical and Personal History

The patient's history is an important part of the diagnosis of pneumonia. The patient should be sure to report any of the following:

• Recent or chronic respiratory infection
• Exposure to people with pneumonia or other respiratory illnesses (such as tuberculosis)
• History of smoking
• Alcohol or drug abuse
• Recent travel
• Occupational risks

Physical Examination

Use of the Stethoscope. The most important diagnostic tool for pneumonia is the stethoscope. Sounds in the chest that may indicate pneumonia are the following:

• Rales (a bubbling or crackling sound). Rales on one side of the chest and rales heard while the patient is lying down are strongly suggestive of pneumonia.
• Rhonchi (abnormal rumblings indicating the presence of thick fluid).
• Percussion. The physician will also use a test called percussion, in which he or she taps the chest lightly. A dull thud, instead of a healthy hollow-drum-like sound, indicates certain conditions that suggest pneumonia. These conditions include including consolidation (a condition in which the lung becomes firm and inelastic), and pleural effusion (fluid build-up in the space between the lungs and the lining around it).

Laboratory Tests for Diagnosing Infection and Identifying Bacterial Agents

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 cause of the infection. Standard lab tests used to help diagnose pneumonia include:

Sputum Tests. Looking at the mucus (sputum) sample coughed up from the lungs tells the doctor how sever the disease is. Only a sputum sample will reveal the infecting organism.

The patient coughs as deeply as possible. (A shallow cough produces a sample that usually only contains normal mouth bacteria.) Some patients may need to inhale a saline spray to help them produce an adequate sample. In some cases, a tube will be inserted through the nose down into the lower respiratory tract to induce a deeper cough.

The physician will check the sputum for:

• Blood, which means there is an infection
• Color and consistency -- if it is yellow, green, or brown, infection is likely

A good sputum sample is sent to the laboratory for analysis to look for the presence of bacteria and determine if they are gram-negative or positive.

Blood Tests. The following blood tests may be performed:

• White blood cell count (WBC). High levels indicate infection.
• Blood cultures. Cultures are done to detect the specific organism causing the pneumonia, but they usually can not distinguish between harmless and dangerous organisms. They are accurate in only 10% to 30% of cases. Their use should generally be limited to severe cases.
• Detection of antibodies to S. pneumoniae. Researchers are using specialized techniques to detect antibodies to S. pneumoniae. Antibodies are immune factors that target specific foreign invaders. It is unclear if these techniques are accurate.
• Polymerase Chain Reaction (PCR). In some difficult cases, PCR may be performed. A test makes multiple copies of the genetic material (the RNA) of a virus or bacteria so it becomes detectable.

Urine Tests. A urine test called NOW can detect S. pneumonia within 15 minutes. It may identify up to 77% of pneumonia cases and may rule out the infection in 98% of patients who do not have S. pneumonia. However, it may not be very useful in diagnosing S. pneumoniae as a cause of pneumonia in children.

Laboratory Tests for Less Common Organisms

If uncommon organisms, such as Legionella, Mycoplasma, and Chlamydia organisms, are strongly suspected, more advanced laboratory tests may be used:

• Specialized techniques can detect antibodies to the organisms in blood samples, but these antibodies, such as those responding to Mycoplasma or Chlamydia, are not present early enough in the course of pneumonia to permit prompt diagnosis and treatment.
• PCR is useful for identifying certain atypical strains, including Mycoplasma and Chlamydiapneumoniae and possibly Haemophilus influenzae type b, but it is expensive.
• A urine test can be used to diagnose some cases of Legionnaires' disease.
• Specialized tests called DNA probes are being developed to detect these organisms in respiratory secretions.

Chest X-Rays and Other Imaging Techniques

X-Rays. A chest x-ray is nearly always taken to confirm a diagnosis of pneumonia.

X-rays are a form of electromagnetic radiation (like light). They are of higher energy, however, and can penetrate the body to form an image on film. Structures that are dense (such as bone) will appear white, air will be black, and other structures will be shades of gray depending on density. X-rays can provide information about obstructions, tumors, and other diseases, especially when coupled with the use of barium and air contrast within the bowel.

A chest x-ray may reveal the following:

• White areas in the lung called infiltrates, which indicate infection
• Complications of pneumonia, including pleural effusions and abscesses

Other Imaging Tests. Computed tomography (CT) scans or magnetic resonance imaging (MRI) scans may be useful in some circumstances, especially when:

• X-ray results are unclear
• Patients do not respond to antibiotics
• Complications occur
• Patients have other serious health problems

Click the icon to see an image of a CT scan.

CT and MRI can help detect the presence of 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.

Invasive Diagnostic Procedures

Invasive diagnostic procedures may be required when:

• Patients have life-threatening complications
• Standard treatments have failed for no known reason
• AIDS or other immune problems are present

Invasive procedures include:

Thoracentesis. If a doctor detects pleural effusion during the physical exam or on an imaging study, and suspects that empyema (pus) is present, a thoracentesis is performed.

• Fluid in the pleura is withdrawn using a long thin needle inserted between the ribs.
• The fluid is then sent to the lab for multiple tests.

Complications of this procedure are rare, but include collapsed lung, bleeding, and introduction of infection.

Bronchoscopy. A bronchoscopy is done in the following way:

• The patient is given a local anesthetic, supplementary oxygen, and sedatives.
• The physician inserts a fiberoptic tube into the lower respiratory tract through the nose or mouth.
• The tube acts like a telescope into the body, allowing the physician to view the windpipe and major airways and look for pus, abnormal mucus, or other problems.
• The doctor removes specimens for analysis and can also treat the patient by removing any foreign bodies or infected tissue encountered during the process.

Click the icon to see an image of bronchoscopy.

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 allergic reactions to the sedatives or anesthetics, asthma attacks in susceptible patients, and bleeding. Fever may follow the procedure.

Lung Biopsy. In very severe cases of pneumonia or when the diagnosis is unclear, particularly in patients with damaged immune systems, a lung biopsy may be required. A lung biopsy involves taking some tissue from the lungs and examining it under a microscope.

A 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 lung aspiration, lung puncture, thoracic puncture, transthoracic needle aspiration, percutaneous needle aspiration, and needle aspiration. It is a very old procedure that is not done often any more, particularly in children, since 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.

Ruling Out Other Disorders that Cause Coughing or Affect the Lung

Common Causes of Persistent Coughing. Over 30 million people seek medical help each year for persistent coughing, which is nearly always temporary and harmless when other symptoms, such as fever, are not present. The four most common causes of persistent coughing are asthma, postnasal drip, gastroesophageal reflux disease (GERD), and chronic bronchitis. Other obvious 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 microbes that cause pneumonia can cause chronic bronchitis, and symptoms of the two disorders are often similar. They include fatigue, coughing, fever, and production of sputum. There are significant differences between chronic bronchitis and pneumonia:

• Patients with bronchitis are less likely to have wheezing, shortness of breath, chills, very high fevers, and other signs of severe illness.
• Those with pneumonia usually cough up heavy sputum, which is also more likely to contain blood.
• X-rays of patients with bronchitis are unlikely to show fluid or consolidation in the lung.

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). Asthmatic symptoms from occupational causes can cause persistent coughing, which is usually worse during the work week. Tests called the methacholine inhalation challenge and pulmonary function studies may be effective in diagnosing asthma.

Anthrax. Because of current terrorist concerns, it is important to differentiate between anthrax and community-acquired pneumonia. According to one study, people with inhalation anthrax are more likely to have rapid heart rate and less likely to have headache, nasal symptoms, and muscle aches than those with pneumonia. Laboratory studies with anthrax also show high hematocrit and low albumin and sodium levels. Certain chest x-ray findings also raise the likelihood of anthrax.

Other Disorders that Affect the Lung. Many conditions mimic pneumonia, particularly in hospitalized patients. They include:

• Tuberculosis
• Bronchial asthma
• Bronchiectasis, an irreversible widening of the airways, usually associated with birth defects, chronic sinus or bronchial infection, or blockage
• Atelectasis, a collapse of lung tissue
• Heart failure -- if it affects the left side of the heart, fluid-build up can occur in the lungs and cause persistent cough, shortness of breath, and wheezing.
• Severe allergic reactions, such as reactions to drugs
• Acute respiratory distress syndrome (ARDS)
• Lung cancer
• Interstitial pulmonary fibrosis, a non-infectious inflammation of the lung is marked by progressive damage and scarring

Ruling Out Causes in Children. Important causes of coughing in children at different ages include:

• Asthma
• Physical abnormalities in infants under 18 months
• Sinusitis in children 18 months to 6 years
• Psychologic causes in older children and adolescents