Sputum analysis

Sputum is a pathological secretion of the respiratory tract, released during coughing and formed when the mucous membrane of the trachea, bronchi and lung tissue is damaged by infectious, physical or chemical agents.

Analysis of sputum in patients with pneumonia in many cases (although not always) allows:

• determine the nature of the pathological process;
• to clarify the etiology of inflammation of the respiratory tract and lung tissue, in particular to identify the causative agent of inflammation;
• determine the main properties of the pathogen, including its sensitivity to antibiotics;
• evaluate the effectiveness of treatment.

Sputum analysis includes:

1. Macroscopic examination (determination of the nature of sputum, its quantity, color, transparency, odor, consistency, presence of impurities and various inclusions).
2. Microscopic examination (determination of cellular and other elements of sputum, as well as study of microbial flora in native and stained smears).
3. Microbiological research (identification and study of the properties of the suspected pathogen).

Chemical examination of sputum has not yet become widespread in clinical practice, although it also has a certain diagnostic value.

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Collection of sputum for examination

Sputum for examination is collected in the morning on an empty stomach after preliminary thorough rinsing of the mouth and throat with boiled water. Sometimes it is recommended to rinse the mouth with a 1% solution of aluminum alum after this.

The patient coughs up sputum directly into a clean, dry glass container with a tightly closing lid. If a microbiological examination of the sputum is planned, it is coughed up into a sterile Petri dish or other sterile container. It is important to warn the patient that when collecting sputum, saliva getting into the samples sent to the laboratory can significantly change the results of the study. Only freshly secreted sputum is sent to the laboratory, since its prolonged standing, especially at room temperature, leads to autolysis of cellular elements and proliferation of microflora. If necessary, short-term storage of sputum in the refrigerator is allowed.

General properties of sputum

Amount of sputum

The amount of sputum usually fluctuates between 10 and 100 ml per day. Little sputum is secreted in acute bronchitis, pneumonia, congestion in the lungs, at the beginning of an asthma attack. At the end of an asthma attack, the amount of sputum secreted increases. A large amount of sputum (sometimes up to 0.5 l) can be secreted in pulmonary edema, as well as in suppurative processes in the lungs, provided that the cavity communicates with the bronchus (with an abscess, bronchiectasis, pulmonary gangrene, with a tuberculous process in the lung, accompanied by tissue decay). It should be borne in mind that a decrease in the amount of sputum secreted in suppurative processes in the lungs can be both a consequence of the abating inflammatory process and a result of a violation of the drainage of the purulent cavity, which is often accompanied by a deterioration in the patient's condition. An increase in the amount of sputum may be regarded as a sign of deterioration in the patient's condition if it depends on an exacerbation, for example, of a suppurative process; in other cases, when an increase in the amount of sputum is associated with improved drainage of the cavity, it is regarded as a positive symptom.

Color of sputum

Most often, sputum is colorless, the addition of a purulent component gives it a greenish tint, which is observed in lung abscess, pulmonary gangrene, bronchiectasis, pulmonary actinomycosis. When fresh blood appears in sputum, sputum is colored in various shades of red (sputum in hemoptysis in patients with tuberculosis, actinomycosis, lung cancer, lung abscess, pulmonary infarction, cardiac asthma and pulmonary edema).

Rusty-colored sputum (in cases of lobar, focal and influenza pneumonia, in cases of pulmonary tuberculosis with caseous decay, pulmonary congestion, pulmonary edema, in cases of pulmonary anthrax) or brown-colored sputum (in cases of pulmonary infarction) indicates that it contains not fresh blood, but rather its decay products (hematin).

Sputum that is secreted during various pathological processes in the lungs, combined with the presence of jaundice in patients, can have a dirty green or yellow-green color.

Canary yellow sputum is sometimes observed in eosinophilic pneumonia. Ochre sputum may be produced in pulmonary siderosis.

Blackish or grayish sputum occurs when there is an admixture of coal dust and in smokers.

Some medications can color sputum; for example, rifampicin colors the discharge red.

The smell of phlegm

Sputum usually has no odor. The appearance of odor is facilitated by a violation of the outflow of sputum. It acquires a putrid odor with an abscess, gangrene of the lung, with putrefactive bronchitis as a result of the addition of a putrefactive infection, bronchiectasis, lung cancer complicated by necrosis. A peculiar fruity smell of sputum is characteristic of an opened echinococcal cyst.

Sputum stratification

When standing, purulent sputum usually separates into 2 layers, putrefactive sputum - into 3 layers (upper foamy, middle serous, lower purulent). The appearance of three-layer sputum is especially characteristic of gangrene of the lung, while the appearance of two-layer sputum is usually observed in lung abscess and bronchiectasis.

Sputum reaction

Sputum usually has an alkaline or neutral reaction. Decomposed sputum acquires an acidic reaction.

Character of sputum

• Mucous sputum is secreted in acute and chronic bronchitis, asthmatic bronchitis, tracheitis.
• Mucopurulent sputum is characteristic of lung abscess and gangrene, silicosis, purulent bronchitis, exacerbation of chronic bronchitis, staphylococcal pneumonia.
• Purulent-mucous sputum is characteristic of bronchopneumonia.
• Purulent sputum is possible with bronchiectasis, staphylococcal pneumonia, abscess, gangrene, and actinomycosis of the lungs.
• Serous sputum is secreted during pulmonary edema.
• Serous-purulent sputum is possible with a lung abscess.
• Bloody sputum is released during pulmonary infarction, neoplasms, pneumonia (sometimes), lung trauma, actinomycosis and syphilis.

It should be noted that hemoptysis and blood in sputum are not observed in all cases of pulmonary infarction (in 12-52%). Therefore, the absence of hemoptysis does not give grounds to refuse the diagnosis of pulmonary infarction. It should also be remembered that sputum analysis with the appearance of abundant blood is not always due to pulmonary pathology. For example, gastric or nasal bleeding can simulate pulmonary hemorrhage.