A sputum fungal smear is a laboratory test ordered when a doctor suspects that a fungus (a yeast or mold) may be causing a patient’s lung infection. The test is also known as a fungal wet prep or a KOH test (where KOH refers to a potassium hydroxide solution).
Fungi are microorganisms. The sputum fungal smear is one of the best ways to find out if your respiratory illness is caused by a fungus, and if so, what kind. Identifying the microorganism helps your doctor provide the proper treatment.
People with weakened immune systems are especially vulnerable to fungal lung infections. This includes those with AIDS, HIV, or cancer, or people who take immunosuppressant treatments, such as chemotherapy, or transplant antirejection drugs.
Fungal lung infections cause pneumonia- or flu-like symptoms, including:
If left untreated, some species of fungi can also cause meningoencephalitis, which is a serious inflammation of the brain and central nervous system. Symptoms include:
- stiff neck
- mental changes such as confusion and changes in personality from mild to severe
It is important to see a doctor right away if you have symptoms of meningoencephalitis. This disease is serious and can cause permanent neurological damage if left untreated.
If you are very sick, you may already be in the hospital. If so, the bedside nurse will help you cough up sputum to send to the laboratory for the test. If you have trouble coughing up sputum on your own, the nurse may have you breathe steam (hot, moist air) to moisten your airways.
If you are sick at home, you will need to collect the sputum sample yourself.
Keep in mind, however, that sputum from deep inside your lungs isn’t the same as saliva. Sputum is mucus, and is 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 the first thing in the morning. This makes the test more accurate. Do not eat or drink anything in the morning before collecting your sample. Your doctor will provide a sterile sample cup. Don’t open the cup until you are 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 until the cup is filled to the marker (approximately 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.
Tip: 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.
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 first thing in the morning.
Bronchoscopy is a simple procedure that takes about 30 to 60 minutes. It is often done in the physician’s office, and the patient usually remains awake.
Do not take medicines that thin your blood the day before your bronchoscopy. These medicines include aspirin, ibuprofen (Motrin, Advil), and naproxen (Aleve). You may take acetaminophen (Tylenol) if needed for pain. You will also be asked not to eat or drink anything the night before the procedure.
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 attend 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 (pneumothorax, which results in a little air being released between the lung and chest wall, and usually fixes itself), bronchial spasms (a sudden clenching of the muscles in the bronchioles), and irregular heart rhythms.
The sputum fungal smear is a culture. In a laboratory, the sputum sample is inoculated into a plate of nutrient (culture) media. The nutrient media used for this test is designed to retard 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, a susceptibility test may also be ordered to determine the best antifungal agent for treating the infection. The susceptibility 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.
Although there are more than 50,000 species of fungi, only about 200 cause diseases in humans. Of these, 25 species commonly cause infections (AACC, 2011). There are even fewer fungi species that cause lung infections.
Most fungi grow in moist places, and the lungs are a perfect host environment. From the lungs, infection can spread to the deep tissue and cause systemic diseases, such as septicemia (bacterial blood infection) and meningoencephalitis (brain and central nervous system inflammation).
Fungal lung infections usually start when a person breathes the microscopic spores into their lungs. Most people are not affected and 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.
Common fungal lung infections include the following:
Aspergillus is a common fungus found in our homes and outdoors. Most people breathe these spores into their lungs every day without being affected. But there are two serious lung infections at-risk people can get from this fungus:
- Allergic bronchopulmonary aspergillosis (ABPA) causes allergic reactions (wheezing and coughing), especially in people who have asthma or cystic fibrosis.
- Invasive aspergillosis can disseminate (spread) throughout the body, damaging the lungs and vital organs, especially in people with weak immune systems.
Blastomyces dermatitidis thrives in decomposing wood and leaves in moist forest environments. The symptoms of blastomycosis, the resulting infection, are similar to the flu, including fever, chills, cough, muscle aches, joint pain, and chest pain. If not treated, the infection can spread to other parts of the body, including the skin and bones.
Coccidioides immitis causes coccidioidomycosis, also known as valley fever. The fungus grows in the dust and soil in the southwestern United States, Mexico, and South America. It is a common cause of pneumonia in these areas. Advanced disease symptoms include skin lesions, meningitis, bone/joint infections, and chronic pneumonia.
People most at risk:
- have a weak immune system
- are of African American or Filipino descent
- are in their third trimester of pregnancy
Cryptococcus neoformans is found in soil all over the world. It rarely causes infections in healthy people, but is a leading cause of death in people who have HIV/AIDS (CDC, 2012). Cryptococcus can cause pneumonia-like symptoms, spread to other parts of the body, and cause life-threatening illness. Symptoms include difficulty breathing, wheezing, fast heartbeat, and fever. If left untreated, cryptococcus can cause meningoencephalitis with symptoms of fever, lethargy, headache, mental changes, and stiff neck. It can also damage the skin, eyes, bones, and joints.
Histoplasma capsulatum is found in the air and soil around large mounds of bird or bat droppings. Breathing the spores causes histoplasmosis, a pneumonia-like illness that can become serious if not treated. Up to 25 percent of HIV/AIDS patients who live in areas where the fungus is found develop histoplasmosis (CDC, 2012). If untreated, it can spread from the lungs to other organs of the body. Some people also experience joint pain.
In people who have a healthy immune system, most fungal lung infections clear up within one month without treatment.
In immune-compromised people, fungal lung infections can become severe. Antifungal medications may need to be continued for three months to several years. During treatment, immunosuppressant drugs should be stepped down or discontinued to help the body fight the infection.