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A sputum culture is
a test to detect and identify bacteria or
fungi (plural of fungus) that are infecting the lungs
or breathing passages. Sputum is a thick fluid produced in the lungs and in the
airways leading to the lungs. A sample of sputum is placed in a container with
substances that promote the growth of bacteria or fungi. If no bacteria or
fungi grow, the culture is negative. If organisms that can cause infection
grow, the culture is positive. The type of bacterium or
fungus will be identified with a microscope or by chemical tests.
If bacteria or fungi that can cause infection grow in the culture, other
tests may be done to determine which antibiotic will be most effective in
treating the infection. This is called susceptibility or
This test is done on
a sample of sputum that is usually collected by coughing. For people who can't
cough deeply enough to produce a sample, they can breathe in a mist solution to
help them cough.
A sputum culture is done to:
Do not use mouthwash before collecting a
sputum sample because it may contain antibacterial substances that could affect
bronchoscopy will be used to collect your sputum
sample, your doctor will tell you how soon before the test to stop eating and
drinking. Follow the instructions exactly about when to stop eating and drinking, or your surgery may be canceled. If your doctor has instructed you to take your medicines on the day of surgery, please do so using only a sip of water.
Tell your doctor
if you have recently taken any antibiotics.
Usually, the sputum sample is collected
early in the morning before you eat or drink anything. In some cases
(especially if you may have tuberculosis), three or more morning samples may be
If you wear dentures, you will need to remove them before
collecting a sputum sample. Then rinse your mouth with water, take a deep
breath, and then cough deeply to produce a sample of sputum. The health
professional collecting the sample may tap on your chest to help loosen the
sputum in your lungs before you cough. If you still have trouble coughing up a
sample, you may be asked to inhale an aerosol mist to help you cough.
Some people may need bronchoscopy to collect a sputum sample. During
bronchoscopy, a thin, lighted tube (bronchoscope) is inserted through your
mouth or nose into the airways leading to your lungs. You will be given
medicine that numbs your throat and nose so you do not feel discomfort from
the bronchoscope. You may also be given a sedative to make you sleepy during
the procedure. To collect the sputum sample, a salt solution may be washed into
the airway and then suctioned into a container. A small, thin brush may be used
to collect a sample.
A sputum sample can also be collected using
suction. During this procedure, a soft, flexible tube (called a nasotracheal
catheter) is inserted through the nose and down the throat. Suction is applied
for up to 15 seconds to collect the sputum sample. This method of collecting a
sputum sample is often used for people who are very sick or unconscious.
sputum sample is collected, it will be placed in a container with substances
(growth medium or culture medium) that promote the growth of infecting
organisms (bacteria or fungi). Bacteria usually need 2 to 3 days to grow. Fungus often takes a week or longer to grow. The organism that causes
tuberculosis may take 6 weeks to grow. Any bacteria or fungi that grow will be
identified under a microscope or by chemical tests. Sensitivity testing, to
determine the best antibiotic to use against the organism that grows, often
takes 1 to 2 more days.
If you have discomfort when taking a deep
breath or when coughing, obtaining a sputum sample may be uncomfortable. If you
need to inhale the aerosol mist to produce a sputum sample, you will often feel
a deep, uncontrollable urge to cough.
During bronchoscopy or
collection of a sputum sample using a catheter, you may feel a strong urge to
cough as the bronchoscope or catheter passes into the back of your throat. You
may also feel as if you cannot breathe. Try to relax and breathe slowly while
the bronchoscope or catheter is in place. If you are given medicine to numb
your throat and nose, you may feel as if your tongue and throat are swollen and
that you cannot swallow.
Your throat may feel sore following bronchoscopy
or collection of a sputum sample using a nasotracheal catheter.
you have severe
bronchitis, you may find it hard to breathe
during collection of a sputum sample using a nasotracheal catheter.
A sputum culture is a test to detect and
identify bacteria or
fungi that are infecting the lungs or breathing
passages. Some types of bacteria or fungi grow quickly in a culture and some
grow slowly. Test results may take from one day to several weeks, depending on
the type of infection suspected. Some organisms (such as Chlamydophila pneumoniae and mycoplasma) do not grow in a
standard culture and need a special growth medium to be detected in a sputum
Sputum that has passed through
the mouth normally contains several types of harmless bacteria, including some
types of strep (Streptococcus) and staph (Staphylococcus). The culture should
not show any harmful bacteria or fungi. Normal culture results are
Harmful bacteria or fungi are
present. The most common harmful bacteria in a sputum culture are those that
tuberculosis. If harmful bacteria or fungi grow, the culture
If test results point to an infection, sensitivity testing
may be done to determine the best antibiotic to kill the bacteria or fungus.
Reasons you may not be able to
have the test or why the results may not be helpful include:
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis:
Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.
November 1, 2012
Adam Husney, MD - Family Medicine & Robert L. Cowie, MB, FCP(SA), MD, MSc, MFOM - Pulmonology
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