Sputum analysis: microscopy and cellular composition
The study of respiratory secretions begins with a macroscopic evaluation, followed by microscopy of native and stained material. The basic staining method is the Gram stain.
The analysis of cells and specific inclusions helps determine the nature of the pathological process:
- Neutrophilic leukocytosis indicates a bacterial infection (e.g., pneumonia or bronchiectasis). Culture on nutrient media is mandatory for the precise selection of an antibiotic.
- Eosinophils serve as a marker of allergic inflammation. In bronchial asthma, the preparation often reveals the classic triad: eosinophils themselves, Curschmann spirals (mucous casts of spastic small bronchi), and Charcot-Leyden crystals (crystallization products of enzymes from destroyed eosinophils).
- Erythrocytes indicate fresh bleeding from the vessels of the bronchi or lungs.
- Siderophages ("heart failure cells") are macrophages that have engulfed hemoglobin derivatives. Their appearance indicates venous congestion in the pulmonary circulation against the background of left ventricular failure.
Special Ziehl-Neelsen staining and repeated cultures on elective media are used to detect Mycobacterium tuberculosis.
Analysis of bronchoalveolar lavage fluid (BALF)
This method is based on studying the washings from the walls of subsegmental bronchi. It provides a detailed picture of the condition of the deep respiratory tract.
Normally, the cytogram of a non-smoker looks as follows: up to 90% of the cells are alveolar macrophages, 7–12% are lymphocytes, 1–5% are bronchial epithelial cells, and band neutrophils are present in minimal quantities (1–2%).
The diagnostic value of BALF is immense. For example, in sarcoidosis, there is a sharp predominance of lymphocytes over neutrophils. In immunodeficiency states (including HIV infection), lavage analysis helps identify opportunistic pathogens such as Pneumocystis and pathogenic fungi.
Pleural fluid analysis
Normally, there is practically no fluid in the pleural cavity, and it is not removed during puncture. Obtaining any volume of punctate is a sign of pathology. Laboratory diagnostics begins with the evaluation of physical properties: transparency, odor, and color (the fluid can be turbid, purulent, chylous, or bloody).
The key task is differential diagnosis between a transudate and an inflammatory exudate:
| Parameter | Exudate (inflammation) | Transudate (non-inflammatory effusion) |
|---|---|---|
| Specific gravity | > 1,015 | < 1,015 |
| Protein level | > 2,5% | < 2,5% |
| Fluid protein / Plasma protein | > 0,5 | < 0,5 |
| Rivalta test | Positive (seromucin "cloud") | Negative |
During microscopy of the punctate, a predominance of neutrophils indicates purulent inflammation, while lymphocytes indicate an immune response. The presence of erythrocytes often accompanies pleural tumors or trauma (hemothorax), and atypical cells suggest mesothelioma.
Instrumental methods as a supplement to laboratory tests
Laboratory tests are always interpreted together with the results of visualization and functional tests.
- High-resolution computed tomography (HRCT) with a slice thickness of 1–2 mm serves as the "gold standard" for diagnosing disseminated processes and allows for a highly detailed evaluation of focal formations.
- Invasive interventions (bronchoscopy, thoracoscopy, mediastinoscopy, and lymph node biopsy) are used to obtain tissue and cellular material for subsequent cytologic and morphologic examination.
- Functional diagnostics is focused on assessing pulmonary function testing (PFT) to understand the degree of functional impairments.
Briefly: answers to topical questions
What macroscopic parameters are evaluated in a general sputum analysis?
Macroscopic examination of sputum evaluates its physical properties and visual characteristics.
- Character — mucous, serous, mucopurulent, or purulent.
- Quantity — varies from 10 to 500 ml or more per day.
- Color — colorless, yellowish, greenish, yellow, rusty, gray, or black.
- Transparency — presence or absence of turbidity.
- Odor — detection of an unpleasant, putrid, or foul odor.
- Consistency — liquid, viscous, or semi-liquid.
- Impurities and inclusions — presence of blood, air bubbles.
- Layering — formation of two or three layers upon standing (sediment, liquid, foam).
What pathological inclusions can be found in sputum during lung tissue destruction?
During lung tissue destruction, specific fibrous structures can be detected in the sputum.
- Elastic fibers — thin, double-contoured, convoluted threads with dichotomous division at the ends. Their detection is a formidable sign of lung parenchyma breakdown, which is typical for lung abscess, pulmonary gangrene, tuberculosis, and disintegrating cancer.
What parameters are evaluated during the macroscopic examination of pleural fluid?
Macroscopic examination (evaluation of physical properties) of pleural fluid assesses the visual characteristics and basic physicochemical parameters of the punctate.
- Appearance — includes the evaluation of transparency and color (clear, turbid, purulent, bloody, chylous).
- Odor — presence or absence of odor.
- Specific gravity — a physical indicator for differential diagnosis.
- Protein level — to determine the nature of the effusion (transudate or exudate).
The specific triad of sputum elements in bronchial asthma is easy to remember: Eosinophils (the cellular basis of allergy), Charcot-Leyden crystals (products of their breakdown), and Curschmann spirals (spastic casts of the bronchi).
Class and exam questions
Why is the Rivalta test used in pulmonology?
This is a historical method based on adding the punctate to an acetic acid solution. The formation of a turbid "cloud" (precipitation of seromucin) confirms that the obtained fluid is an inflammatory exudate.
What does the appearance of siderophages in a sputum analysis indicate?
Siderophages, or "heart failure cells," indicate blood congestion in the pulmonary circulation. Their detection is characteristic of left ventricular failure and decompensated heart defects.
What is the value of high-resolution computed tomography (HRCT)?
HRCT uses slices only 1–2 mm thick, making it the "gold standard" for detailed evaluation of focal infiltrates, changes in the bronchi and pleura, and the diagnosis of disseminated lung lesions.
What else to study on this topic
- Methodology and algorithms for assessing pulmonary function testing (PFT)
- Radionuclide diagnostic methods and lung scintigraphy
- Specifics of contrast methods: angiopulmonography
- Features of culture on elective media when tuberculosis is suspected
- The role of endoscopic methods in obtaining a biopsy specimen
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