What Is a Sputum Fungal Smear?
Your doctor may order a sputum fungal smear if they suspect
that a fungus (a yeast or mold) may be causing your lung infection. The test is
also known as a fungal wet prep or a KOH test.
Fungi are microorganisms. The sputum fungal smear is one of
the best ways to find out if a fungus is causing your respiratory illness. This
test can also identify the specific strain of fungus that’s causing it.
Identifying the microorganism helps your doctor provide the best treatment.
Fungal Lung Diseases
Although there are more than 50,000 species of fungi, only
about 200 cause diseases in humans. Of these, 25
species commonly cause infections. There are even fewer fungi species that
cause lung infections.
Most fungi grow in moist places, and the lungs are a perfect
host environment. The infection can spread from the lungs to the deep tissue
and cause systemic diseases, such as septicemia and meningoencephalitis.
Fungal lung infections usually start when a person breathes
the microscopic spores into their lungs. Most people are not affected and some experience
only moderate flu-like symptoms. They usually get well on their own without
treatment. However, people with weak immune systems can get seriously ill.
How to Collect a Sample of Your Sputum
You will need to collect a sample of your sputum to send to
a laboratory for testing.
The night before the test, drink lots of fluids, such as
water or tea. This will help your body make more sputum overnight. Collecting
your sputum in the morning makes the test more accurate. More bacteria are
present early in the morning.
Keep in mind that sputum from deep inside your lungs isn’t
the same as saliva. Sputum is mucus. It’s usually colored and thick in
consistency, especially when there is infection in the lungs. Saliva comes from
your mouth and is clear-colored and thin.
Plan to collect sputum after waking up in the morning. This
makes the test more accurate. Don’t eat or drink anything before collecting
your sample. Your doctor will provide a sterile sample cup. Don’t open the cup
until you’re ready to collect the sample.
To collect a sputum sample:
- Brush your teeth and rinse your mouth (don’t use
- Take a couple of long, deep breaths.
- Breathe in deeply again and cough hard until
sputum comes up.
- Spit out the sputum into the sample cup.
- Keep coughing up sputum (while taking breaks if
needed) until the cup is filled to the marker (about 1 teaspoon).
- Screw on the cup lid and wash and dry the
outside of the cup.
- Write your name and the date on the cup label.
Take the sample to the clinic or laboratory, as instructed. The
sample can be refrigerated for up to 24 hours, if needed. Do not freeze it or
store it at room temperature.
If you can’t cough up sputum, try breathing the steam from
boiling water, or take a hot, steamy shower. The sputum must come from deep
inside your lungs for the test to be accurate.
If you still cannot cough up sputum, your doctor will do a
bronchoscopy to collect sputum directly from your lungs.
How the Doctor Collects Sputum
A bronchoscopy is a simple procedure that takes about 30 to
60 minutes. It’s often done in your doctor’s office while you remain awake.
Do not take medicines that thin your blood the day before
your bronchoscopy. These medicines include:
- ibuprofen (Motrin, Advil)
- warfarin (Coumadin)
- naproxen (Aleve)
You may take pain-relievers such as acetaminophen (Tylenol)
if needed. You will also be asked not to eat or drink anything the night before
A bronchoscopy is performed as follows:
- A local anesthetic will be sprayed into your
nose and throat to numb them.
- You might be given a sedative to help you relax,
or medication to put you to sleep.
- General anesthesia is not usually needed for
- The bronchoscope is a soft, small-circumference
tube with a light and magnifying glass on the end.
- The doctor feeds the scope through your nose or
mouth into your lungs.
- Using the magnifying glass, the doctor can see
into the lungs and use the scope to remove a sample of your sputum.
- A nurse will monitor you during and after the
procedure until you are fully awake.
- For safety, you should have someone else drive
Risks of Sputum Sample Collection
There are no risks in collecting a sputum sample yourself.
You might feel light-headed when coughing deeply. Rare risks of bronchoscopy
- allergic reactions to sedatives
- tearing in the lung, or pneumothorax
- bronchial spasms, a sudden clenching of the
muscles in the bronchioles
- irregular heart rhythms
Lab Analysis of Your Sputum Sample
In the laboratory, your sputum sample is introduced into a
plate of nutrient media. The nutrient media is designed to slow the growth of
bacteria, while feeding the growth of fungi microorganisms. Fungi grow slowly,
so it may take several weeks to culture and get the test results back.
Later, your doctor may also order a susceptibility test to
determine the best antifungal agent for treating the infection. This test is
done on the microorganisms themselves, grown from the original sputum sample
During treatment, your doctor may collect more sputum
samples and have them tested to make sure your medicines are working to
eradicate the fungi.
Understanding Your Test Results
Abnormal results commonly mean that one of these fungi is
- Aspergillus (causes aspergillosis)
dermatitidis (causes blastomycosis)
immitis (causes coccidioidomycosis)
- Cryptococcus neoformans (causes
capsulatum (causes histoplasmosis)
Normal test results mean you do not have a fungal lung
In people who have a healthy immune system, most fungal lung
infections clear up within one month without treatment.
In people with weak immune systems, fungal lung infections
can become severe. Antifungal medications may need to be used for three months
to several years. During treatment, immunosuppressant drugs should be stepped
down or discontinued to help the body fight the infection.