What is a sputum Gram’s stain?
A sputum Gram’s
stain is a laboratory test that allows your doctor to diagnose
a bacterial infection in your respiratory tract. They may order it if you have
symptoms of a respiratory infection that might be caused by bacteria. It’s the
most common preliminary test beyond a chest X-ray for pneumonia and other
respiratory infections, and can help your doctor promptly prescribe a treatment
The test is sometimes called a Gram’s stain
of sputum. It’s named after its inventor, Hans Christian Gram.
When is the test ordered?
Your doctor may order a sputum Gram’s stain
to help identify the cause of pneumonia. This is an infection that can affect
your lower respiratory tract. It’s often caused by microorganisms, like
bacteria, viruses, or fungi.
The symptoms of pneumonia can range from
moderate to life-threatening, and include:
- shortness of breath
- rapid breathing
- chest pain
- muscle aches
- nausea and vomiting
- sputum that’s colored or has an odor
- respiratory failure
- shock (severely low blood pressure)
Children under the age of 5, older adults
over the age of 65, and people with a weak immune system are at heightened risk
of developing pneumonia.
What does the procedure involve?
To complete a sputum Gram’s stain, your
doctor will need to a collect a sample of your sputum and send it to a
laboratory for testing.
Sputum is a mixture of saliva and mucus that
you cough up from your respiratory tract. It’s usually colored and thick in
consistency, especially when you have an infection in your lungs.
Plain saliva comes
from your mouth and is usually clear.
Your doctor may ask you to collect a sample
of your own sputum, but if you can’t they may collect one using a bronchoscopy.
If you’re very sick, you may be in the
hospital when your doctor orders a sputum Gram’s stain. A nurse will help you
cough up sputum. If you have trouble, they may give you a breathing treatment
to help loosen the sputum in your airways.
If you’re at home, your doctor may ask you to
collect the sputum sample yourself. They will give you a sterile sample cup to
use. Wait until you’re ready to collect your sample before opening the lid.
The night before you provide a sample, try to
drink lots of fluids like water or tea. This will help your body make more
sputum. Collect your sample first thing in the morning, before eating or
drinking anything. There tends to be more bacteria present at this time and can
help ensure accurate test results.
To provide a sample of your sputum:
- Brush your teeth and rinse your mouth. Don’t use antiseptic
- Take a couple of long, deep breaths. Then breathe deeply and cough
hard until sputum comes up.
- Spit out the sputum into your sample cup. Keep coughing up sputum
until the cup is filled to the marker, which should equal approximately 1
- Screw the lid onto the cup and wash and dry the outside of it.
Write your name and the date on the label.
- Take the sample to the clinic or
laboratory, following your doctor’s instruction. You can refrigerate it for up
to 24 hours if needed, but you shouldn’t freeze it or store it at room
If you can’t cough up enough sputum, try
breathing steam in from boiling water, or take a hot steamy shower. The sputum
sample must come from deep inside your lungs for the test to be accurate.
If you still can’t cough up enough sputum,
your doctor will likely do a bronchoscopy to collect sputum directly from your
Bronchoscopy is a simple procedure that usually takes about 30 to 60 minutes.
You will probably stay awake for it.
Ask your doctor if you should do anything to
prepare for your bronchoscopy. They may ask you to avoid taking medicines that
raise your risk of bleeding, such as aspirin and warfarin, the day before your
procedure. Your doctor may also ask you to avoid eating and drinking anything
the night before your procedure.
To perform a bronchoscopy, your doctor or nurse will
spray a local anesthetic into your nose and throat. They might also give you a
sedative to help you relax, or medication to put you to sleep, but general
anesthesia isn’t required.
doctor will feed a bronchoscope through your nose or mouth into your lungs. This
is a soft, narrow tube with a light and magnifying glass on the end.
doctor will use the scope to look into your lungs and collect a sample of your
sputum to send to the lab for testing.
be monitored until you’re fully awake. To be safe, you should have someone drive
you home afterward.
How is your sputum sample analyzed?
At the laboratory, a technician will analyze
your sputum sample using a sputum Gram’s stain.
They will place a thin layer of your sputum
on a slide and allow it to dry. Then they will treat the slide with a special
staining agent that’s sensitive to peptidoglycan.
Peptidoglycan is a polymer made from amino acids and sugars. It’s found in the
cell walls of bacteria, and helps laboratory staff learn if bacteria are
present in your sputum.
After adding the staining agent, the
laboratory technician will examine the slide under a microscope. The Gram’s
stain doesn’t allow them to identify every specific type of bacteria, but it
can help them tell if there are bacteria with thick cell walls or thin cell
Bacteria with thick cell walls will produce a
Gram-positive result. Bacteria with thin cell walls will produce a
The test can also help the laboratory
technician detect the presence of fungi in your sputum.
And the technician will also look for white
blood cells in your sputum, which is a sign of infection.
What do the results mean?
If the test
results from your sputum Gram’s stain are abnormal, it means that bacteria and
white blood cells have been detected. The bacteria found will be Gram-positive
Common Gram-positive bacteria detected by the
Common Gram-negative bacteria detected by the
- E. coli
- Klebsiella species
- Proteus species
- Pseudomonas aeruginosa
A normal test result means that few white
blood cells and no bacteria have been found in your sputum sample, and your
symptoms may be due to other causes.
Depending on your test results, your doctor
may prescribe a treatment plan or order more tests. If you have a bacterial
lung infection, they will likely prescribe antibiotics.
This will probably be enough to treat your
infection if you have a healthy immune system.
In some cases, bacterial pneumonia can be
more severe and even life-threatening. It can be particularly serious for older
adults and others with weakened immune systems. Sometimes, severe cases of
pneumonia can lead to:
- collection of fluid in your lungs
- scarring in your lungs, which may make you susceptible to future
- abscesses in your lungs
- respiratory failure
- sepsis, which is a bacterial blood infection
diagnosis can help your doctor prescribe a treatment plan, which may help
improve your outlook.
There are very few risks associated with
collecting a sample of your sputum. You might feel slightly light-headed when
you cough deeply, or feel discomfort in your lungs or throat.
Side effects from bronchoscopy are also rare,
but can include:
- pneumothorax, which happens when air is released into the space
between your lung and chest wall
- bronchial spasms, which can occur when muscles in your bronchioles
- irregular heart rhythms.
- allergic reactions to sedatives
your doctor for more information about the potential benefits and risks of
providing a sputum sample.
A sputum Gram’s stain is a quick, low-risk
laboratory test. Your doctor can use the results to help diagnose the cause of
respiratory symptoms. In particular, the presence of disease-causing bacteria.
Determining the cause of your symptoms can
help your doctor prescribe an appropriate treatment plan. Your treatment plan
will vary, depending on your diagnosis.