The color of sputum or phlegm, which is the mucus and sometimes pus discharge expectorated from the respiratory tract, is often an indication of the type of respiratory disease that gives rise to sputum production. By examining the type of sputum and noting the color as well as the presenting signs and symptoms, a differential diagnosis may be reached prior to laboratory tests and examination – sputum cytology and culture. A thorough case history and complete physical examination is also necessary.
Ideally, the morning sputum specimen should be examined as this provides a more vivid indication of the cause. Sputum samples that are coughed or spat up during the course of the day may lack the features that would provide a clue to the disease process and be tainted by foods and drinks, especially those rich in artificial colorants.
Meaning of Different Sputum Colors
As mentioned under the Types of Sputum, the discharge is a combination of mucus produced in the respiratory tract and saliva from the mouth. It also contains microorganisms, immune cells, cellular debris, dust and possibly even blood components or whole blood (plasma and blood cells). Depending on the quantity of these components and disease process, the sputum color may vary between :
Clear, White, Gray Sputum
Clear sputum is considered as normal, however, there are many conditions that may cause excessive sputum production. A profuse amount of clear sputum should therefore be considered as abnormal.
- Pulmonary edema (fluid in the lungs) – clear, white or pink frothy sputum
- Viral respiratory tract infections – clear to white (acute)
- Chronic bronchitis (COPD) – clear to gray
- Asthma – white to yellow (thick)
Yellow colored sputum is due to the presence of white blood cells, particularly neutrophils and eosinphils. These cells are often present in chronic inflammation, allergic and infectious causes. With infections, it is often in the acute setting that yellow sputum is evident due to the presence of live neutrophils. With allergic conditions, particularly airway hypersensitivity, the yellowish sputum is due to the presence of eosinophils.
- Acute bronchitis – white to yellow
- Acute pneumonia – white to yellow
- Asthma – white to yellow (thick)
Green mucus is indicative of a long-standing, possibly chronic, infection. The color is a result of the breakdown of neutrophils and the release of verdoperioxidase / myeloperioxidase, an enzyme that is present within these cells. It may also be seen in long standing non-infectious inflammatory conditions. With infections, the green sputum will be more purulent (large amounts of pus) while in non-infectious inflammatory conditions, the green sputum will be more mucoid (large amounts of mucus).
- Pneumonia – white, yellow or green
- Lung abscess – green, sudden accumulation of large amount of sputum if the abscess ruptures
- Chronic bronchitis – clear, grey to green (infection)
- Bronchiectasis, cystic fibrosis – green
Brown and Black Sputum
Brown or black sputum is an indication of ‘old blood’ and the color may be due to the breakdown of red blood cells thereby releasing hemosiderin (from hemoglobin). Certain organic and non-organic dusts may also cause a brown to black discoloration of the sputum.
- Chronic bronchitis – green, yellow, brown (infection)
- Chronic pneumonia – white, yellow, green to brown
- Coal worker’s pneumoconiosis – brown to black
- Tuberculosis – red to brown or black
- Lung cancer – red to brown to black
Red, Pink and Rust-Colored Sputum
Red sputum is usually an indication of whole blood that is more profuse than bleeding in pink colored sputum. It may completely discolor the mucus or appear as streaks or spots. Pink sputum is also a sign of bleeding but usually of smaller quantities that may stain or streak the sputum. Rust colored sputum is also due to the bleeding although the clotting process may have commenced and the red blood cells may have broken down.
- Pneumococcal pneumonia – rusty-red
- Lung cancer – pink to red (frothy) progressing to brown or black
- Tuberculosis – bright red streaks progressing to fully red sputum (hemoptysis)
- Pulmonary embolism – bright red blood (acute)