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.

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.

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 antiseptic mouthwash).
  • 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.

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:

  • aspirin
  • 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 the procedure.

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 bronchoscopy.
  • 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 you home.

There are no risks in collecting a sputum sample yourself. You might feel light-headed when coughing deeply. Rare risks of bronchoscopy include:

  • allergic reactions to sedatives
  • infection
  • bleeding
  • tearing in the lung, or pneumothorax
  • bronchial spasms, a sudden clenching of the muscles in the bronchioles
  • irregular heart rhythms

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 you provided.

During treatment, your doctor may collect more sputum samples and have them tested to make sure your medicines are working to eradicate the fungi.

Abnormal results commonly mean that one of these fungi is present:

  • Aspergillus (causes aspergillosis)
  • Blastomyces dermatitidis (causes blastomycosis)
  • Coccidioides immitis (causes coccidioidomycosis)
  • Cryptococcus neoformans (causes cryptococcosis)
  • Histoplasma capsulatum (causes histoplasmosis)

Normal test results mean you do not have a fungal lung infection.

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.