Sputum Culture and Analysis
the liquid substance that comes from your respiratory tract when you cough. In
addition to mucus, sputum contains many materials that are not visible to the
naked eye. It often consists of bacteria, cellular fragments, blood, and pus.
of your sputum can give your physician useful information for screening or
diagnosing bacterial infections in the respiratory system.
What Does the Test Diagnose?
culture and analysis is used to diagnose lower respiratory tract infections
caused by bacteria or fungi. It can be used to identify causes of the following
bacteria are found on your sputum culture, the culture can be used to diagnose
and identify appropriate treatment for:
of chronic obstructive pulmonary disease (COPD)
in cystic fibrosis patients
How to Prepare for the Test
Check with your physician to find
out if you should temporarily discontinue taking any medication prior to giving
a sputum sample. Antibiotics, anti-inflammatory drugs, and steroids can affect
the results of a sputum culture.
You may be advised to drink
plenty of water and other liquids the night before giving your sputum sample.
This will make it easier to cough up a sample the next morning. Prior to the
test, you will be asked to rinse out your mouth.
How Is the Sample Collected?
The collection of a sputum sample
may be done in a physician’s office, laboratory testing site, or hospital. In
some cases, you may be instructed to collect your own specimen at home. A
sputum sample collected at home should be taken to a laboratory as quickly as
possible to ensure that it remains fresh.
You will get the best results if
you provide a sample first thing in the morning, before you have food or drink.
This will provide a sample with the sputum from the deepest part of your chest.
Prior to providing the sample,
you will be instructed to rinse out your mouth with water or saline. This clears
out microorganisms from your mouth. You will be asked to breathe deeply and then
deeply cough. As you cough up the sputum, you will deposit it into a sterile collection
For best results, it is important
to ensure that the sample you provide includes sputum, not just saliva. The
saliva will contain the microorganisms found in your mouth, not necessarily
those causing an infection in your lungs. Saliva is watery; sputum usually is
yellow and thick. In cases of infection, the sputum may be green or flecked with
If you are unable to produce a
sample of sputum, a sample can be induced by your physician or lab technician.
You may be asked to inhale sterile saline or a glycerin aerosol, which will
help loosen the sputum deep in your lungs.
How Is the Test Done?
Your sample will be taken to a
laboratory for sputum culture and analysis.
A Gram stain test will identify
that the sample is adequate and contains enough bacterial cells to proceed. This
test involves placing a portion of the sample on a slide. The slide is stained
with red and purple dyes and examined with a microscope.
The test may also help identify the type of
bacteria that may be present. By looking at the bacteria’s reaction to the dyes
and other characteristics, a technician can identify the bacteria as either
gram-positive or gram-negative.
If adequate, the sample will be
placed in a special plate that encourages the growth of the bacteria or fungi.
This is the sputum culture. A bacterial infection may require up to 48 hours to
grow. It may take a week or more for fungi to reproduce.
Sputum analysis involves using
chemical tests and microscopes to examine the different types of bacteria and
fungi present. Part of this identification process involves classifying the bacteria
as either normal or disease-causing organisms. The disease-causing organisms
are then tested to determine what antibiotics will work best to treat them.
What Are the Benefits of the Test?
Providing a sample for a sputum
culture and analysis is noninvasive and requires little time. However, it can
provide valuable information to your physician in identifying and diagnosing
the cause of a respiratory infection. The results can help your physician
determine an appropriate antibiotic or other course of treatment. It also can
help your physician determine if an ongoing treatment is effective.
For some individuals, a bacterial
respiratory infection can cause serious consequences. If you are elderly, have
a suppressed immune system, lung damage, or a lung condition such as COPD or
cystic fibrosis, finding prompt, accurate treatment is critical.
What Are the Risks of the Test?
Having a sputum sample collected for culture
and analysis by coughing is safe. If you have a respiratory infection, the
coughing required to produce the sample might cause discomfort.
How Are the Results Interpreted?
Your physician will receive the
results of the sputum culture and analysis. Results may be available within a
few days. However, some types of fungi may take a week or longer to grow for
If your results are “negative” or
normal, there was no evidence of disease-causing bacteria or fungi in your
However, if symptoms persist, it
may indicate the presence of a viral infection or other microorganism that
wasn’t adequately represented in the sputum sample. Some types of organisms
can’t be grown and identified with sputum culture, so additional testing may be
If your results are “positive” or
abnormal, your physician will use the information in the sputum analysis to choose
the most effective course of antibiotic treatment and therapy for your lung