This is the examination of sputum (the fluid that is secreted by cells in the lower respiratory tract such as the bronchi and the trachea) under a microscope to detect abnormal or cancerous cells. Sputum, or phlegm, differs from saliva, in that it contains cells that line the respiratory passages.
The sputum cytology test is a rapid and inexpensive test. However, it is not always precise. It sometimes gives false positive (that is, the test indicates cancer when there is no cancer) and false negative (that is, the test indicates there is no cancer when cancer is present). While the rate of false-positive is low (1%), the rate of false negatives can be as high as 40% of tests.
Sputum cytology test is more effective in the diagnosis of squamous cell lung cancers, which start in the central airways, than in the diagnosis of other types of lung cancer, particularly those that are located in more distant areas of the lungs. While it is able to detect approximately 71% of tumors that are centrally located, it detects less than 50% of tumors located in the periphery (that is, outer regions) of the lungs. Due to the limitations of sputum cytology test, especially giving false-negative results, additional testing is usually recommended when the test comes back with a negative result (that is, showing no cancer) in patients where lung cancer is suspected, to conclusively determine the presence or absence of lung cancer.
In the case of positive results (that is, showing cancer), the sputum cytology test does not provide enough information for doctors to enable them to determine the exact type of lung cancer a patient has. So a biopsy is usually required to get a good sample of the tumor and identify the type of lung cancer.
Why it’s required
Sputum test is required for a number of reasons, such as
- To diagnose lung cancer.
- To diagnose non-cancerous lung conditions, like pneumonia, inflammatory diseases, tuberculosis, or asbestosis (the build-up of asbestos fibers in the lungs).
- To diagnose asthma.
It may also be required if any of the following is being experienced
- Lungs pain. That is pain that begins in the region of the lungs.
- Cough, especially when it’s a persistent cough.
- Shortness of breath.
- Detected abnormality on a chest x-ray or CT scan.
- When there’s exposure to tuberculosis.
There is no special preparation. However, if there is anything you need to take care of, your doctor will fill you in.
The first in the sputum test is sample production. You will produce three sputum samples over a period of 3 days. You will be given a container to produce the sputum sample into. The container may contain a small amount of liquid in it. This is a fixative. It helps preserve the sample. It should be noted that the samples for a sputum test are best collected early in the morning, right after waking up, for a better result. After which the samples are submitted to the doctor’s office or the laboratory.
The sample submitted for the sputum test is examined under a microscope. Before viewing with a microscope, a special staining procedure and other techniques will be carried out to further define what is being seen. If during the microscopic analysis bacteria are present, the sample will then be cultured to determine exactly which bacteria are causing an infection.
After the analysis, the result comes back with normal findings or abnormal findings seen. For normal findings, this means that only normal lung cells were present in the sputum sample submitted for the sputum test.
For abnormal findings, this means that abnormal lung cells were present in the sputum sample submitted for the sputum test. These abnormal cells signify that the lung is not in healthy condition, and these could be conditions such as inflammation, asbestosis, pneumonia, or even lung cancer.