Sputum Cytology: Purpose, Procedure, Results and Lung Cancer Testing

Why is Sputum Cytology Done and What Does it Tell You?

photo of sputum on a tissue
What is sputum cytology. Wikimedia Commons/User Zhangmoon618

If your doctor has recommended a sputum cytology, what does this entail? How is the sample taken? When is this test recommended and what are the limitations in using it as a screen for lung cancer?

Definition: Sputum Cytology

Sputum cytology refers to the examination of sputum (mucus) under a microscope to look for abnormal or cancerous cells.

Sputum, or phlegm, refers to the fluid that is secreted by cells in the lower respiratory tract such as the bronchi and the trachea.

Sputum differs from saliva, in that it contains cells that line the respiratory passages.

Sputum Collection

Sputum is usually collected by forcefully coughing into a container, or during a bronchoscopy.   While this procedure has not been found to be an effective screening test for lung cancer, when done on someone with symptoms, it can sometimes result in a diagnosis of lung cancer.

Sputum Cytology Preparation

Before you have your sputum cytology sample taken, your doctor or nurse will give you special instructions to follow. On the day of the procedure, you will want to carefully rinse your mouth and teeth, but it's important to not use toothpaste. You will want to blow your nose prior to the procedure to minimize the amount of upper airway drainage you have.  

When you are doing the procedure, the nurse will help you take deep breaths and expectorate from deep in your chest. It will be important to bring up fluids as if you are coughing rather than spitting.

People often have to attempt getting a sample more than once, as it can be difficult obtaining sputum instead of saliva.

Sputum Cytology: Under the Microscope

Once the sputum sample is obtained, it is looked at under the microscope. Special stains may be done, and other techniques to further define what is being seen.

If bacteria are present, the sample will then be placed in a culture and grown (a sputum culture) to determine exactly which bacteria are causing an infection.

Indications: Reasons to Do a Sputum Cytology Test

Sputum cytology may be ordered for a range of symptoms. Some of these include:

Conditions That May be Diagnosed

Sputum cytology may be done to diagnose a wide array of conditions including;

Pneumonia: In this procedure, a pathologist may see bacteria. Based on the particular shapes of the bacteria (whether they look round or like rods,) and what they look like with different stains, your doctor can choose the best antibiotic for beginning treatment. Pneumonia is often first treated in this way since the exact organisms present may not be determined for another 48 hours or more (when the sputum culture results become available.) A sputum cytology can narrow down the choices of a correct antibiotic or combinations of antibiotics considerably.

Lung cancer: While not a good screening test for lung cancer, if lung cancer cells are found in sputum they can help diagnose the disease.

A sputum cytology, however, doesn't give the location of the cancer so further tests will be needed.

Asthma: Sputum cytology can also be done to look for the number of eosinophils in a sample of sputum. Eosinophils are a type of white blood cells that are present in increased amounts with allergies. Recent studies suggest that determining sputum eosinophils is useful when combined with symptoms to tailor the treatment of asthma and reduce the number of asthma exacerbations.

Tuberculosis: A special type of sputum cytology may be done to diagnose tuberculosis.

Sputum Cytology and Lung Cancer

Even though it was found that sputum cytology is not adequate as a screening test, studies are ongoing looking to see what possible role it may have in the diagnosis of lung cancer.

In general, tumors within or near the large airways are more likely to shed cancer cells into the airways that would appear in a sputum sample.

In recent years, the most common types of lung cancer have changed. In years past, squamous cell carcinoma of the lungs and even small cell lung cancer were more common. These cancers tend to grow near the large airways. Now the most common type of lung cancer is lung adenocarcinoma. These cancers tend to grow in the outer regions of the lungs away from the airways. Therefore, it's likely that sputum cytology will play a lesser role in lung cancer detection in the future.

The other reason for a decrease in the need for sputum cytology is that we now do have a screening test for lung cancer which is effective, at least in those who meet the criteria for screening.

Sources:

Petsky, H., Li, A., and A. Chang. Tailored Interventions Based on Sputum Eosinophils versus Clinical Symptoms for Asthma in Children and Adults. Cochrane Database of Systematic Reviews. 2017. 8:CD005603.

U.S. National Library of Medicine. Routine Sputum Culture. Updated 09/05/17. https://medlineplus.gov/ency/article/003723.htm

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