Pneumonia can be hard to diagnose because it may seem like a cold or the flu. You may not realize it's more serious until it lasts longer than these other conditions.
                
Your doctor will diagnose pneumonia based on your medical history, a physical exam, and test results.
                
Medical History
                
Your doctor will ask about your signs and symptoms and how and when they began. To find out what type of germ is causing the pneumonia, he or she also may ask about:
                
Any recent traveling you've done
                
Your hobbies
                
Your exposure to animals
                
Your exposure to sick people at home, school, or work
                
Your past and current medical conditions, and whether any have gotten worse recently
                
Any medicines you take
                
Whether you smoke
                
Whether you've had flu or pneumonia vaccinations
                
Physical Exam
                
Your doctor will listen to your lungs with a stethoscope. If you have pneumonia, your lungs may make crackling, bubbling, and rumbling sounds when you inhale. Your doctor also may hear wheezing.
                
Your doctor may find it hard to hear sounds of breathing in some areas of your chest.
                
Diagnostic Tests
                
If your doctor thinks you have pneumonia, he or she may recommend one or more of the following tests.
                
Chest X Ray
                
A chest x ray is a painless test that creates pictures of the structures inside your chest, such as your heart, lungs, and blood vessels.
                
A chest x ray is the best test for diagnosing pneumonia. However, this test won't tell your doctor what kind of germ is causing the pneumonia.
                
Blood Tests
                
Blood tests involve taking a sample of blood from a vein in your body. A complete blood count (CBC) measures many parts of your blood, including the number of white blood cells in the blood sample. The number of white blood cells can show whether you have a bacterial infection.
                
Your doctor also may recommend a blood culture to find out whether the infection has spread to your bloodstream. This test is used to detect germs in the bloodstream. A blood culture may show which germ caused the infection. If so, your doctor can decide how to treat the infection.
                
Other Tests
                
Your doctor may recommend other tests if you're in the hospital, have serious symptoms, are older, or have other health problems.
                
Sputum test. Your doctor may look at a sample of sputum (spit) collected from you after a deep cough. This may help your doctor find out what germ is causing your pneumonia. Then, he or she can plan treatment.
                
Chest computed tomography (CT) scan. A chest CT scan is a painless test that creates precise pictures of the structures in your chest, such as your lungs. A chest CT scan is a type of x ray, but its pictures show more detail than those of a standard chest xray.
                
Pleural fluid culture. For this test, a fluid sample is taken from the pleural space (a thin space between two layers of tissue that line the lungs and chest cavity). Doctors use a procedure called thoracentesis (THOR-ah-sen-TE-sis) to collect the fluid sample. The fluid is studied for germs that may cause pneumonia.
                
Pulse oximetry. For this test, a small sensor is attached to your finger or ear. The sensor uses light to estimate how much oxygen is in your blood. Pneumonia can keep your lungs from moving enough oxygen into your bloodstream.
                
If you're very sick, your doctor may need to measure the level of oxygen in your blood using a blood sample. The sample is taken from an artery, usually in your wrist. This test is called an arterial blood gas test.
                
Bronchoscopy. Bronchoscopy (bron-KOS-ko-pee) is a procedure used to look inside the lungs' airways. If you're in the hospital and treatment with antibiotics isn't working well, your doctor may use this procedure.
                
Your doctor passes a thin, flexible tube through your nose or mouth, down your throat, and into the airways. The tube has a light and small camera that allow your doctor to see your windpipe and airways and take pictures.
                
Your doctor can see whether something is blocking your airways or whether another factor is contributing to your pneumonia.