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Sputum Culture: Why and How is it Done?

Medically reviewed by Jezreel Esguerra, MD · General Practitioner

Written by Nikita Bhalla · Updated Mar 28, 2023

    Sputum Culture: Why and How is it Done?

    Sputum culture finds the cause behind respiratory infections. Also called phlegm, sputum is the mucus that is produced in the lower air passage of your lungs when you have an infection or any chronic lung issue.

    A lung infection like pneumonia can cause cough and sputum production. Other lung conditions like chronic obstructive pulmonary disease (COPD) and bronchiectasis may likewise cause the phlegm along with cough. 

    This test helps your doctor to know the cause of buildup of sputum in your lungs. Once the cause is detected, your doctor will recommend a suitable treatment for you. 

    Why Is It Done

    Your doctor will suggest a sputum culture to know if fungi or bacteria are the ones responsible for your condition. For example, the test may detect tuberculosis and pneumonia.


    Before the sputum culture, your doctor may give a few instructions and precautions. This will help obtain proper results and prevent false-positive or false-negative results. 

    For this test, you do not require any special preparations. However, your doctor may recommend drinking a lot of water and other fluids the night before the test to make it easier for you to cough up the sputum. 

    Also, before the test, you must inform your doctor about the list of medicines that you are using. It is because certain medicines may interfere with your test results. However, you may stop taking medicines only after your doctor’s recommendation. Do not stop using any drug without consulting your doctor. 

    Apart from the list of prescription and non-prescription drugs, it is best to tell your doctor about any health condition that you have. It is because certain health conditions may cause false-positive or false-negative results. 

    In case you underwent any surgery, including abdominal surgery, tell your doctor beforehand. 

    Understanding Sputum Culture

    A sputum culture result is available in the positive or negative format for the germs that are tested. Once you receive your result, ensure you visit the doctor’s clinic. Your doctor will read the results for you and recommend the suitable treatments for you. 

    Your test results will be available within a few days to a month or two. Generally, your doctor will inform you when you can collect the test results. 

    sputum culture

    Negative sputum culture result

    If you receive a negative test result, it indicates that you do not have any disease-causing germs. 

    Positive test result

    An abnormal sputum culture result is considered positive. A positive result indicates that the test identified the bacteria, virus, or fungus. This may help diagnose the following causes:

    • Tuberculosis
    • A flare-up of chronic obstructive pulmonary disease or cystic fibrosis
    • Lung abscess
    • Pneumonia
    • Sarcoidosis
    • Bronchitis 

    According to your test result, your doctor will suggest suitable treatment and prescribe medication. However, you must know that not all abnormal test results indicate a problem. Your doctor may ask you to repeat the test if your doctor suspects anything suspicious. 

    Do not start any treatment or use any remedy without consulting your doctor. 

    When Should Sputum Culture be Repeated?

    Your doctor may ask you to repeat the sputum culture for the following reasons:

    • If you used mouthwash before the test
    • Not enough sputum sample collected
    • Intake of antibiotics before the test
    • Contamination of your sputum sample

    Apart from these reasons, your doctor may recommend repeating the test to monitor the effects of medicines and treatment on the infection. 


    A sputum culture is simple on your part and does not require any extra efforts. All you need to do is deposit your sputum sample to the lab. Your doctor will ask you to cough deeply to bring sputum mucous from your lungs.

    When someone asks you to cough, you generally give out saliva from the upper airways or mouth. That is not useful for the test. 

    Your doctor may use a few techniques to collect a good sputum sample.

    You will be asked to drink plenty of fluids or water to loosen up the secretions and make it easier for you to cough up sputum. Your doctor may ask you to rinse your mouth to get rid of germs and extra saliva.

    You will put your sputum into a small cup or container. The lab testing needs at least 2 milliliters of sputum. 

    Your doctor may tap on your chest to loosen the sputum if you have issues in getting the sample or enough sample. Your doctor may also suggest inhaling a steam-like mist that helps you to cough up and get sputum. 

    Once you collect enough sputum, your sample will undergo analysis. 

    Deep coughing for the test may cause discomfort. Some people may feel chest discomfort or pain after depositing the sample. 

    However, you must know that there are no major risks associated with a sputum culture. 

    If you underwent any surgery in the past like abdominal surgery, your doctor may ask you to hold a pillow over your stomach before coughing, a technique called splinting. This may minimize abdominal discomfort. 

    If you feel any discomfort that does not ease within a few hours, inform your doctor.


    Hello Health Group does not provide medical advice, diagnosis or treatment.

    Medically reviewed by

    Jezreel Esguerra, MD

    General Practitioner

    Written by Nikita Bhalla · Updated Mar 28, 2023

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