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The goals with testing are to determine the microorganism causing the pneumonia, to limit its spread to other people, to determine the severity of the pneumonia, and to guide treatment. In a significant number of cases, it is not possible to determine the exact cause of acute pneumonia, and treatment is based upon the person's clinical presentation and medical history, the doctor's experience, likely microorganisms present in the community at the time, such as influenza, and on established guidelines for the care of lower respiratory infections. If a person's symptoms do not resolve, then additional testing may be performed to help diagnose less common pneumonia causes.

Non-laboratory Tests
The search for the cause of symptoms typically begins with a physical exam. As part of the exam, a doctor listens to a person's lungs for abnormal rumbling, crackling, and bubbling noises that may indicate a lung infection. This is often followed with imaging studies. These may include:

  • Chest X-ray — used to detect and help evaluate the severity of lung infection
  • CT (Computed Tomography) scan — sometimes use to detect and evaluate lung infection and to look for other causes of a person's symptoms

Laboratory Tests
Depending on the affected person's medical history and the signs and symptoms that are present at the time of the physical exam, a number of laboratory tests may be performed to help make a diagnosis.

General laboratory tests may include:

Tests for suspected bacterial pneumonia:

Tests for suspected viral pneumonia:

Other types of tests that may be performed depending on patient history and clinical presentation:

  • Pleural fluid analysis — if fluid has accumulated in the space between the lungs and chest wall, the fluid may be tested to help determine the cause of infection
  • Fungal culture — sometimes ordered when a fungal infection is suspected
  • Mycoplasma testing — blood test or special culture to help diagnose a mycoplasma infection
  • Legionella testing — blood test for the specific antigen, culture or molecular test to diagnose a suspected Legionella infection

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