Pneumonia - Diagnosis - Diagnosis

Your doctor will diagnose pneumonia based on your medical history, a physical exam, and test results. Sometimes pneumonia is hard to diagnose because your symptoms may be the same as a cold or flu. You may not realize that your condition is more serious until it lasts longer than these other conditions. 

Medical history and physical exam

Your doctor will ask about your signs and symptoms and when they began. Your doctor will also ask whether you have any risk factors for pneumonia. Your doctor also may ask about: 

  • Exposure to sick people at home, school, or work or in a hospital
  • Flu or pneumonia vaccinations
  • Medicines you take
  • Past and current medical conditions and whether any have gotten worse recently
  • Recent travel
  • Exposure to birds and other animals
  • Smoking

During your physical exam, your doctor will check your temperature and listen to your lungs with a stethoscope.

Diagnostic tests and procedures

If your doctor thinks you have pneumonia, he or she may do one or more of the following tests.

  • Chest X-ray to look for inflammation in your lungs. A chest X-ray is often used to diagnose pneumonia.
  • Blood tests, such as a complete blood count (CBC) to see whether your immune system is fighting an infection.
  • Pulse oximetry to measure how much oxygen is in your blood. Pneumonia can keep your lungs from moving enough oxygen into your blood. To measure the levels, a small sensor called a pulse oximeter is attached to your finger or ear.

If you are in the hospital, have serious symptoms, are older, or have other health problems, your doctor may do other tests to diagnose pneumonia.

  • Blood gas test. If you are very sick, your doctor may need to measure your blood oxygen levels using a blood sample from an artery, usually in your wrist. This is called an arterial blood gas test.
  • Sputum test. Your doctor may test a sample of sputum (spit) or mucus from your cough to find out what germ is causing your pneumonia.
  • Blood culture. This test can identify the germ causing your pneumonia and also show whether a bacterial infection has spread to your blood.
  • Polymerase chain reaction (PCR) test. This test quickly checks your blood or sputum sample to find the DNA of germs that cause pneumonia.
  • Bronchoscopy. If your treatment is not working well, your doctor may use this procedure to look inside your airways. During the procedure, your doctor may also collect samples of your lung tissue and fluid from your lungs to help find the cause of your pneumonia.
  • Chest computed tomography (CT) scan. This test can show how much of your lungs are affected by pneumonia. It can also show whether you have complications such as lung abscesses or pleural disorders. A CT scan shows more detail than a chest X-ray.
  • Pleural fluid culture. In this procedure, called thoracentesis, your doctor uses a needle to take a sample of fluid from the pleural space between your lungs and chest wall. The fluid is then tested for bacteria.