by Carlos R. Salvarezza
Examination of the sputum is an important method for diagnosing certain diseases of the respiratory system. Bacteria, Koch bacilli, cells, fungi, parasites and other elements can be investigated.
Bacteria . Under normal conditions in the mouth and in the pharynx there is a mixed flora made up of saprophytic bacteria, and some eventually pathogenic. The expectoration has the disadvantage of becoming contaminated with these microorganisms when it passes through the oropharynx. This is the reason why the value of sputum in the etiological diagnosis of bacterial infections of the lower airways is controversial. We consider that this method serves to establish a presumptive etiological diagnosis as long as certain conditions are met: having more than 25 leukocytes and less than 10 desquamation cells per small magnification field, common ciliated epithelium, alveolar macrophages, predominance of a typical bacterium morphology and the finding of elastin fibers.
Koch bacilli. The finding of Koch bacilli certifies the diagnosis of tuberculosis, but its absence does not exclude it, since a concentration of 10,000 bacilli per milliliter of expectoration is needed for them to be detected.
Sometimes a sputum sample is falsely positive because the smear contains acid-fast particles. These particles, which may resemble tuberculosis bacilli, are: waxes, oils, acid-fast saprophytic bacilli, some species of nocardia, spores of bacilli subtilis, some fibers, coniferous pollens.
Cells . Neoplastic cells . In patients with bronchogenic carcinoma, it is possible to detect neoplastic cells in 85% of the cases located in the large bronchi, and in 50% when the location is peripheral, provided that at least three samples of sputum are examined. It is difficult to determine the histological type to which these cells belong, and exceptionally a primitive neoplasm can be differentiated from a secondary one. On occasions, neoplastic cells can be confused with abnormal macrophages and with some cells with degenerative processes, causing false positives.
Neutrophilic leukocytes . They are frequent in the bronchial secretions of asthmatics.
Other cells . Hematicas (erythrocytes) in hemoptic sputum, anthracotic (macrophages with dark granules) in people who aspirate carbon particles, cardiac (macrophages with ferruginous pigments) in left heart failure.
Fungi . Normally in the expectoration, fungal filaments can be found, which is why their finding causes a diagnostic problem in terms of determining their pathogenicity or not. In the sputum of pulmonary mycoses it is possible to detect blastomyces, coccidiodes, aspergillos, histoplasmas, cryptococci, monilias.
Parasites . In pulmonary hydatidosis, echinococcal hooks can be seen in the sputum when a cyst ruptures in a bronchus.
Currently the systematic investigation of Pnemocytis carinii has significantly increased its positive results due to the frequency of acquired immunodeficiency syndrome (AIDS).
Other items . The finding of “sulfur” granules is characteristic of actinomycosis; Charcot-Leyden crystals (fusiforms, shiny) are typical of bronchial asthma; Curschmann's coils (spiral-shaped filaments) are rarely found in asthma; Dittrich's plugs (whitish granules) can be seen infrequently in severe bacterial infections.