A sputum sample is a gooey substance that often comes up from your chest when you have an infection in your lungs or airways. It is mostly made up of white blood cells that fight infection. A sputum culture is a laboratory test that looks for germs that cause infection. The test checks for bacteria or another type of organism that may be causing an infection in your lungs or the airways leading to the lungs. During the test, a sample of sputum is obtained by coughing deeply and expelling the material that comes from the lungs into a sterile cup. The sample is then sent to a laboratory where it is watched for two to three days or longer to see if bacteria or other disease-causing germs grow. The test helps identify the bacteria or other types of germs that are causing an infection in the lungs or airways. A sputum culture is often done with another test called a Gram stain, which checks for bacteria at the site of a suspected infection or in body fluids such as blood or urine. The test can help identify the specific type of infection you may have. A sputum culture is often done if you have symptoms of pneumonia or another serious infection of the lungs or airways, such as coughing up a lot of sputum, fever, chills, shortness of breath, chest pain that gets worse when you breathe deeply or cough, fatigue, or confusion, especially in older people.