A sputum stain for Mycobacteria is a laboratory test performed on a sample of your sputum, or phlegm. It’s also known as an acid-fast bacillus (AFB) stain or a tuberculosis (TB) smear.

A doctor typically orders the test to determine if a person has tuberculosis (TB) or another type of mycobacterial infection.

If you’re already taking medication for TB or another mycobacterial infection, your doctor might order the test to find out if your medication is working.

Your doctor will order this test if they think you have a mycobacterial infection.

Mycobacteria are a type of microorganism with nearly 100 known species. The most common type is Mycobacterium tuberculosis, which causes TB. The general symptoms of TB include:

  • coughing up blood or mucus
  • a lack of appetite
  • weight loss
  • weakness
  • fatigue
  • a fever
  • chills
  • night sweats

Another fairly common type of this bacteria is Mycobacterium leprae, which causes leprosy, also known as Hansen’s disease. The symptoms of Hansen’s disease include:

  • skin discoloration
  • skin lesions
  • skin nodules
  • skin plaques
  • thickened skin
  • nasal congestion
  • nosebleeds

Except for the two microorganisms that cause TB and Hansen’s disease, most Mycobacteria exist in the water and soil everywhere in the world. These are called nontuberculous mycobacteria (NTM).

NTM live in:

  • city water
  • bayous
  • rivers
  • hot tubs
  • swimming pools
  • yard soil
  • food

Their tough, waxy cell wall makes them resistant to antibacterial agents.

Although NTM are everywhere, most people aren’t affected. People with immunity problems, such as associated with having AIDS, are vulnerable to infection.

Some people can have an infection with no symptoms at all. Other people have infections that cause lung symptoms similar to TB.

Medications can treat these infections, but it often takes more than one medication to cure them.

The night before the test, drink lots of fluids, such as water or tea, to 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.

Either you or your doctor will collect the sputum.

If you’re very sick, you may already be in the hospital. If so, a healthcare provider will help you cough up sputum to send to the laboratory for the test.

If you have trouble coughing up sputum on your own, they may have you breathe steam.

If you’re sick and at home, you’ll need to collect the sputum sample yourself.

Keep in mind that sputum from deep inside your lungs isn’t the same as saliva.

Sputum is mucus, and it’s usually colored and thick in consistency, especially when there’s an infection in your lungs. Saliva comes from your mouth. It’s clear and thin.

Plan to collect sputum first thing in the morning, which makes the test more accurate. Don’t eat or drink anything in the morning before collecting your sample. Your doctor will give you a sample cup that’s sterile. Don’t open the cup until you’re ready to collect the sample.

To collect a sputum sample, you should do the following:

  1. Brush your teeth and rinse your mouth without using antiseptic mouthwash.
  2. Take a couple of long, deep breaths.
  3. Breathe deeply again and cough hard until sputum comes up.
  4. Spit out the sputum into the sample cup.
  5. Keep coughing up sputum until the cup is filled to the marker, which is approximately 1 teaspoon.
  6. Screw on the cup lid, and wash and dry the outside of it.
  7. Write your name, your date of birth, and the date of collection 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. Don’t 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.

Bronchoscopy is a simple procedure that takes about 30 to 60 minutes. It’s often done in the doctor’s office while you’re awake.

Don’t take medications that thin your blood the day before your bronchoscopy. These medications include:

  • aspirin
  • ibuprofen (Motrin, Advil)
  • naproxen (Aleve)

You may take acetaminophen (Tylenol) if needed for pain. You’ll also be asked not to eat or drink anything the night before the procedure.

Bronchoscopy is performed as follows:

  1. A local anesthetic will be sprayed into your nose and throat to numb them.
  2. You might be given a sedative to help you relax or medication to put you to sleep.
  3. General anesthesia isn’t usually needed for bronchoscopy.
  4. The bronchoscope is a soft, small tube with a light and magnifying glass on the end. Your doctor feeds the scope through your nose or mouth and into your lungs.
  5. Your doctor can see into your lungs using a magnifying glass, and they can use the scope to remove a sample of your sputum.
  6. You’ll have a nurse with you during and after the procedure until you’re fully awake.
  7. For safety, you should have someone else drive you home.

Your sputum specimen will be spread on a microscope slide. A staining dye is added to the cells of the specimen and then washed in an acid solution. The cells are then examined under a microscope.

If the cells retain the stain, this means mycobacterium are present. Mycobacteria are usually acid-fast, which means they hold onto the dye when washed in an acid solution.

A culture is another kind of test that may be done.

The sputum specimen is placed into a culture medium, which contains nutrients. The specimen is allowed to grow at room temperature for several days. This makes it possible to see a greater number of bacteria cells to confirm the results.

There are no risks associated with collecting a sputum sample yourself. You might feel lightheaded when coughing deeply.

Rare risks of bronchoscopy include:

  • an allergic reaction to sedatives
  • an infection
  • bleeding
  • bronchial spasms, which involve sudden clenching of the muscles in the bronchioles
  • irregular heart rhythms

A pneumothorax is another rare risk. It involves a tearing in the lung that results in a small amount of air being released between the lung and chest wall. If it’s small, it usually fixes itself.

If your test results are normal, or negative, this means no mycobacterial organisms were found.

If the test is abnormal, it means the stain is positive for one of the following organisms:

  • M. tuberculosis
  • M. leprae
  • nontuberculous bacteria
  • other acid-fast bacteria

Your doctor will advise you on your results. If you need treatment, they’ll tell you about your best options.