The first step in diagnosing pneumonia is to consult a physician. A medical history will likely be taken. A physician will ask questions about symptoms and whether the patient has any history of similar illnesses. A physical examination may also be conducted and the physician may use a stethoscope to listen to the lung sounds. A crackling sound (rales) is usually an indication that there is fluid in the lungs and the patient may have pneumonia.

Other tests may be conducted, including:

• Chest x-ray. The chest x-ray is one of the most accurate methods of diagnosing pneumonia. In people with pneumonia, a shadow can sometimes be seen over the lungs. In some cases, the x-ray may not show signs of pneumonia, even though the patient is displaying clear symptoms. This may happen if the infection is in its early stages or it is affecting a part of the lung that is not easily seen by the x-ray. The physician may then recommend a CT (computed tomography) scan of the chest to develop a more accurate picture.
  
  
• Sputum culture. A physician may send out a sample of sputum or mucus (the discolored phlegm produced while coughing) to a laboratory to test it for signs of pneumonia germs. These tests are also used to indicate which medications the germs may respond to.
  
  
• Blood tests. In some cases, a complete blood count (CBC) may be conducted to count the number of white blood cells present in the blood. A high number of white blood cells normally means that the body is trying to fight an infection. However, this may not be the case for people with weakened immune systems. Other blood tests may be able to test for other microorganisms in the blood or whether the patient has bacteremia (bacteria in the blood), which is a common complication of some types of pneumonia.
  
  
• Blood oxygen measurement. Pneumonia can affect the absorption rate of oxygen into the bloodstream. To determine if this is occurring to a patient suspected of having pneumonia, a physician may attach a small infrared clip to the finger or the ear. This painlessly measures the amount of oxygen in the blood.