What Causes the Amount of Sputum to Increase?

Sputum or phlegm is the mucousy substance secreted by cells in the lower airways (bronchi and bronchioles) of the respiratory tract. It differs from saliva, which is produced higher up, in the mouth. Sputum can be any color including clear, white, yellow, green, pink or red and blood tinged with different medical conditions. In addition to containing dead cells, foreign debris that is inhaled into the lung, and at times, bacteria, sputum contains white blood cells and other immune cells that protect the airway from infections. There are a number of medical conditions that result in increased sputum production. Tests to analyze sputum, such as sputum cytology and sputum cultures may be helpful in diagnosing disease.

Understanding Sputum

As noted above, sputum contains dead cells and debris from the lower respiratory tract, but also plays a role in fighting infection, by trapping bacteria and containing white blood cells to fight them.

Sputum vs Phlegm vs Mucus vs Saliva

Sputum is secreted into the airways (bronchi and bronchioles) of the respiratory tract. Sputum is not the same as saliva, a substance secreted in the mouth to help with digestion. The terms sputum and phlegm are used interchangeably.

The term mucus may sometimes be used instead of sputum, but sputum refers to that mucus specifically secreted in the respiratory tract, whereas mucus may also be produced in the gastrointestinal tract, urological tract, and genital tract.

Source of Sputum

Sputum or phlegm is coughed up from the lower airways in the respiratory tract—the bronchi, bronchioles, and trachea—rather than glands in the mouth and throat. It is produced by cells called goblet cells that line the airway

Contents

Sputum is made up from secretions from cells lining the respiratory tract, dead cells, foreign matter than is breathed into the lungs, such as tar from cigarettes and air pollutants, and white blood cells and other immune cells. In infections, bacteria may also be present in sputum. Blood may also be present in the sputum with lung cancer, trauma to the respiratory tract, damage to the airways, and pulmonary edema.

Function

The thickness of sputum serves to trap foreign material so that the cilia in the airway can clear it from the lungs by moving it up through the mouth where it can be swallowed or coughed out. Sputum also contains immune cells that can serve to kill or engulf bacteria so that they are unable tor remain in the lungs and cause infections.

Tobacco smoke causes the cilia in the airways to become less much mobile (paralyzed). When this occurs, sputum is not moved up towards the mouth by the cilia, and can accumulate in the airways.

What Sputum Colors Mean

Sputum can be many colors and consistency, and these can help define certain conditions. For example:

  • Clear sputum: Clear sputum is usually normal, although it may be increased in some lung diseases. 
  • White or gray sputum: White or grayish tinged sputum can also be normal, but may be present in increased amounts with some lung diseases or precede other color changes associated with other conditions.
  • Dark yellow/green sputum: A type of white blood cells known as neutrophils have a green color to them. These types of white blood cells are attracted to the scene of bacterial infections, and therefore bacterial infections of the lower respiratory tract, such as pneumonia, may result in the production of green sputum. yellow-green sputum is common with cystic fibrosis as well.
  • Brown sputum: Brown sputum due to the presence of tar, is sometimes found in people who smoke. Sputum may also appear brown or black due to the presence of old blood. Brown sputum is also common with "black lung disease." These diseases, called pneumoconioses, occur from inhaling substances like coal into the lungs.
  • Pink sputum: Pink, especially frothy pink sputum may come from pulmonary edema, a condition in which fluid and small amounts of blood leak from capillaries into the alveoli of the lungs. Pulmonary edema is often a complication of congestive heart failure. Pink or blood tinged sputum is commonly caused by tuberculosis worldwide.
  • Bloody sputum: Bloody sputum, even just a trace of blood tinged sputum, should always be evaluated. Coughing up blood (hemoptysis) can be serious, and is the first sign of lung cancer in 7 percent of people. Bloody sputum may also occur with a pulmonary embolism, a condition in which a blood clot in the leg breaks off and travels tot he lungs. Even 1 teaspoon to 2 teaspoons of coughed up blood is considered a medical emergency, and coughing up a fourth of a cup of blood is considered massive hemoptysis and carries a poor prognosis.

Increased Production

Some conditions that result in increased production of sputum include:

  • Chronic bronchitis: Chronic bronchitis results in increased sputum, and in fact, the criteria for a diagnosis of chronic bronchitis includes a daily cough productive of sputum
  • Bronchiectasis: This is a form of chronic obstructive pulmonary disease (COPD) often caused by chronic respiratory infections in childhood.
  • Pulmonary edema
  • Overproduction of sputum can also be caused by smoking and exposure to air pollution

Tests to Evaluate Sputum

Sputum may be analyzed in the lab to determine its contents in order to evaluate infections or look for cancer. Tests may include:

  • Sputum culture: A sputum culture is done by placing a sample of a sputum in a growing media (agar dish) and looking for the presence of growth. This can be done to determine the particular type of bacteria causing pneumonia. Once the bacterial strain is determined, the lab can then do further tests to figure out which antibiotic is most effective against that bacteria (sensitivity testing).
  • Sputum for tuberculosis: A sputum sample may be obtained to look for tuberculosis, though several samples are often needed in order to find one that is diagnostic.
  • Sputum cytology: In sputum cytology a sample of sputum is evaluated under the microscope. This can be done to look for signs of tuberculosis or signs of cancer cells. At one time it was thought that sputum cytology could a screen for lung cancer, but it is not an effective screening tool. If cancer cells are found, however, it can be diagnostic of lung cancer. Further tests will then need to be done to find out the location of the cancer.

Obtaining a sample of sputum (instead of mucus) can be somewhat challenging, as it requires having a person cough up sputum from deep in the lungs.

Decreasing Production

There are a number of ways in which to decrease sputum production, but the most important step is to diagnose and treat the underlying cause. With air pollution and smoking, the underlying cause is the body's attempt to rid itself of foreign matter, and an overproduction of sputum is a normal response. In that case removing the source is the best approach. Medications that may help decrease sputum include aerosol treatments and expectorants. Treatments such as postural drainage may be effective in some situations.

A Word From Verywell

Sputum is a substance produced by the respiratory tract which contains a combination of cells, foreign matter, and white blood cells. The color, consistency, and amount of sputum can be important in diagnosing a number of different medical conditions. Visualization of sputum may also aid in the diagnosis of conditions such as tuberculosis and even lung cancer. Though an increased amount of sputum can be very annoying, it is often the body's attempt to rid itself of material (such as tar and other foreign matter) that could otherwise lodge in and damage the airways.

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