Exams and Tests

Your doctor will usually diagnose pneumonia by using your medical history, a physical exam, and a chest X-ray. Based on the medical history and physical exam, your doctor may start your treatment right away without doing other tests. The need for more tests often depends on how severe your symptoms are, your age, and your overall health. In general, the sicker you are, the more tests you will have. This is especially true for older adults and infants.

A chest X-ray is almost always done to check for changes in the lungs that may mean pneumonia and to look for other causes of your symptoms. However, an X-ray does not always show whether you have pneumonia, especially if the X-ray is done when you first get sick.

In some cases, the X-ray results may:

• Suggest the type of organism (bacterial, viral, or fungal) causing pneumonia.
• Show complications of pneumonia.
• Show conditions that may occur with pneumonia, such as fluid in the chest cavity or a collapsed lung.
• Reveal another condition, such as heart failure, lung cancer, or acute bronchitis.

If you are very ill, have severe shortness of breath, or have a condition that increases your risk (such as asthma or chronic obstructive pulmonary disease), your doctor may examine your mucus.

• In a Gram stain, you cough up a sample of mucus (sputum) that is then treated with a material (Gram stain) and examined under a microscope. This test may indicate what type of organism (bacterium or fungus) is causing the pneumonia. This test can help your doctor choose the best medicine for your infection.
• In a sputum culture and sensitivity, a sample of mucus is placed in a container with substances that will make bacteria or fungi grow. If bacteria or fungi grow, your doctor can identify them and choose the correct treatment. Unfortunately, getting lung mucus that has not been contaminated with throat or mouth mucus is difficult. So, the results are not always helpful in identifying the cause of pneumonia. This test may be less useful if you have already started using antibiotics.

If you have severe pneumonia, you may need other tests, including tests to check for complications and to determine how well your immune system is working.

A urine test is available that may identify within 15 minutes whether you are infected with Streptococcus pneumoniae, one of the main causes of bacterial pneumonia, or Legionella pneumophila, the bacterium that causes Legionnaires' disease and sometimes can cause pneumonia.

Although experts consider the test to be useful for the identification of Legionella pneumophila, doctors generally do not use it to identify Streptococcus pneumoniae.⁴ But it may be useful in adults with severe pneumonia and when a Gram stain has not identified the bacteria.⁵

In people with impaired immune systems, pneumonia may be caused by other organisms, including some forms of fungi, such as Pneumocystis jiroveci (formally called Pneumocystis carinii). This fungus frequently causes pneumonia in people who have AIDS. Some doctors may suggest an HIV test if they think that Pneumocystis jiroveci is causing the pneumonia.