What It Is Kids with cystic fibrosis (CF) tend to get frequent respiratory infections, sometimes caused by bacteria or fungi. A sputum (mucus) CF respiratory screen or culture helps doctors detect and identify these bacteria or fungi so they can prescribe the most effective antibiotics to target a specific infection. Why It's Done A sputum culture can help identify specific causes of infections in the lungs and airways. Such infections can lead to coughing that produces yellow, greenish, or blood-tinged sputum, in addition to fever and difficulty breathing. Preparation Before the test, be sure to tell the doctor whether your child has taken antibiotics recently. The best time for testing is usually in the morning, before your child has had anything to eat or drink. Also, make sure your child doesn't use mouthwash before the test because it may contain antibacterial ingredients that could affect results. The Procedure Your child will be asked to rinse his or her mouth out with water, then breathe deeply and cough deeply to produce sputum from the airway. You or the health professional helping your child may need to tap gently on your child's chest to loosen the sputum in the lungs. If your child can't produce a sample, the lab technician may need to use a tongue depressor to stimulate a cough, or your child may need to inhale a mist solution to help produce a cough. If your child is scheduled for a bronchoscopy (a test done with a small telescope to evaluate the upper airway and bronchi), a sputum screen is likely to be done at this time. What to Expect Your child may feel mild discomfort when taking a deep breath or coughing. If your child inhales the mist solution, the urge to cough may be strong. It may take several attempts at coughing to produce the amount of sputum needed for the test. Getting the Results The sputum sample is collected into a sterile container and sent to a laboratory. The sample is then placed on a special plate that enables growth of certain bacteria and fungi if an infection is present. If your child has a bacterial infection, the organisms may need 48 hours to grow. Fungi need a week or longer. These organisms will be seen under a microscope or through chemical tests. If the tests show an infection, another 1-2 days may be needed to choose the best antibiotic to treat it. Risks Coughing to produce the sputum specimen may be mildly uncomfortable, but there are no risks associated with this procedure. Helping Your Child Explaining the test in terms your child can understand might help ease any fear. Also reassure your child that the procedure doesn't hurt. If You Have Questions If you have questions about the sputum respiratory screen, speak with your doctor. Back to Articles Related Articles Cystic Fibrosis Cystic fibrosis (CF) is a genetic disorder that affects the lungs and digestive system Kids who have it can get lung infections often and have trouble breathing. Read More Cystic Fibrosis Cystic fibrosis (CF) is an inherited disease that causes the body to produce mucus that's extremely thick and sticky. It mainly affects the lungs and the pancreas, causing serious breathing and digestive problems. Read More Germs: Bacteria, Viruses, Fungi, and Protozoa Germs are the microscopic bacteria, viruses, fungi, and protozoa that can cause disease. Read More Cystic Fibrosis (CF) Chloride Sweat Test Is your child scheduled to have a sweat test? Find out how this test is performed and how it's used to diagnose cystic fibrosis. Read More Lungs and Respiratory System Each day you breathe about 20,000 times. Find out more about the lungs and breathing process. Read More Lungs and Respiratory System By the time we're 70 years old, we will have taken at least 600 million breaths. All of this breathing couldn't happen without the respiratory system. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.