Sputum
PKGhatak, MD
Sputum is the other name of spit. The word sputum is derived from Latin Spuere. The aristocratic name of spit is Phlegm. That word is derived from the Greek word Phlegein. The old French language modified it to Flume, the old English named it Fleem and finally modern English is Phlegm.
In India Phlegm is the answer to a trivia question - what is that substance that the poor discard it indiscriminately and the rich carefully save it in between the folds of monogrammed handkerchief and tuck it carefully in their pocket/purse.
When all the humor is removed the sputum is made up of mostly water, a bit of mucin, and 1 % salt. Mucin is secreted by the Goblet cells of the respiratory tract. Chemically mucin is a polymer of glycoproteins. Mucin has a complex structure. The core is composed of structurally strong protein molecules composed of amino acids serine, proline, and threonine and the core protein is bonded to various oligosaccharides by O-glycosidic linkages. Then the pattern is repeated several times, the sequence of which is highly variable in length and amino acid composition. 90 % of mucin is carbohydrate. Mucin is highly hygroscopic and keeps particulate matter and microorganisms wrapped up tightly. In addition, the sputum contains a few shredded epithelial cells, WBCs, lysosomes, IgA antibodies, lactoferrin and usual respiratory and oral flora.
For the medical profession, the sputum is nothing to sneer about. Whatever is responsible for a disease of the lung, sooner or later it has to come out dead or alive, with the sputum. Naturally, the sputum examination provides a direct clue of an illness and is also used to monitor the progress of the disease.
Let's look at the sputum.
Generally, sputum is collected in the morning. The patient is instructed to rinse their mouth with water then cough vigorously for several minutes and collect sputum in a sterile container provided by the lab. The sputum should contain secretion from deep inside the lung and not saliva. If the sample contains only a few WBCs and more than 20 epithelial cells per low power field, the lab rejects the specimen and marks "inadequate sample" and requests for resubmission. In some lung diseases, the patient can hardly raise the sputum. To facilitate sputum collection, inhalation of nebulized 3% saline is used, at times assisted by chest percussion with cupped hands. If that fails the samples are obtained at a bronchoscopic examination.
Sputum is examined for color, smell, amount, consistency, frothiness, foaminess, cellular debris, crystals, malignant cells, microorganisms, parasites, fungal spores, and filaments, amoeba. Then smears are made, properly stained and examined under a microscope to identify microorganisms. Cultures are planted on proper media for bacteria and fungi. Special methods are used for malignant cells to obtain a better yield. Sputum is handled separately for tuberculosis. Alkaline digestion of gastric aspirate sample then centrifuged. The sediment is used for culture. Sputum from gastric content is another source in patients who are unable to raise sputum as in young children and unconscious patients.
Color of sputum and its significance:
The primary reason for sputum examination is an infection of the lungs, other important reasons are hemoptysis and lung cancer. Bacterial pneumonia produces thick yellow-green sputum; the green color is due to the presence of myeloperoxidase and the yellow color is from degenerated neutrophils. Bloody sputum is due to hemorrhage in the lung. (see the section on hemoptysis blog). Red jelly like sputum is from Klebsiella pneumonia. Blood streaking sputum is generally due to cancer of the lung. Rusty color is from Pneumococcal pneumonia. The brown color is from Cancer of the lung and tuberculosis. Grayish white is from dehydration. Pink frothy sputum is due to acute pulmonary edema. White, opaque and scanty sputum is from asthma. Green sputum is from Pseudomonas pneumonia. Black sputum is common in coal miners' pneumoconiosis, Aspergillus niger infection.
Smell of sputum:
The putrid smell is associated with the breakdown of tissues from bacterial enzymes releasing gases containing hydrogen sulfide, aromatic compounds, aldehyde, and ketones. Foul smelling sputum is from anaerobic bacterial infection, usually from a lung abscess, however, infection by anaerobe from gum to lung generates a foul odor. The wet fur smell is from Hemophilus influenza pneumonia. The acrid smell from Bacteroides fragilis. The burnt chocolate smell from Proteus mirabilis pneumonia. some other Proteus species can produce an odor of rotten fish. Dirty sneaker smell from Citrobacter. The fecal odor from Pepto streptococcal infection. Pneumonia from Bacteroides, Proteus, and Peptostreptococcal are rare and seen in immunocompromised patients. The buttery smell is from Streptococcal viridance infection. The musty odor from Streptomyces. The sweet fruity odor from Pseudomonas aeruginosa pneumonia.
Amount of sputum:
COPD patients with pneumonia can produce 100 to 200 ml sputum. Bronchiectasis, in general, produces over 150 ml of sputum a day. Patients with acute left ventricular failure can produce over 150ml of pink frothy sputum. In asthma and in pure pulmonary emphysema only a small amount of sputum is raised.
Consistency:
Watery sputum is just saliva. In a single nodular lesion due to suspected cancer or tuberculosis, no sputum may be generated and collected specimens are watery. Thick yellow sputum indicates bacterial pneumonia, and viral pneumonia can produce light yellow green sputum. Foamy sputum is from air bubbles trapped in the sputum, commonly seen in COPD. White frothy or pink frothy sputum in pulmonary edema. Thick sticky sputum is from Cystic fibrosis. Chocolate mousse sputum from ruptured amoebic liver abscess through the lung.
Parasites in sputum:
Ascaris lumbricoidis is usually coughed up alive and found wiggling in a sputum cup.
Strongyloides stercorales larvae, and hookworm larvae are also seen in heavy infestations.
Parasitic ova: Paragonimus westernanii eggs are a common finding in that fluke infection of the lung.
Schistosoma eggs are occasionally coughed up in liver cirrhosis when a hepatopulmonary shunt is formed.
Entamoeba histolytica in sputum is seen in cases where amoeba invades the lung from the liver through adhesion.
Fungal Filaments:
Pneumonia from Aspergella fumigatus, Candida albicans, Actinomycetes israeli, Nocardia (previously grouped with bacteria Actinomyces) cases sputum contains fungal filaments.
Fungal yeast form: All dimorphic fungi yeast is recovered in the sputum of disseminated infection. These fungi are Histoplasma capsulatum, Blastomycoses brazilancies, Cocciodides immitis, Sporothrix schenkii.
Fungal spores: are seen in Candida, Cryptococcus, Pneumocystis jirovecii lung infection.
Crystal in sputum: Calcium oxalate crystals are a hallmark in Aspergilla pulmonary infiltrative disease. The byproduct of growing Aspergilla is oxalic acid which combines with serum calcium to form crystals. Charcot Leyden crystals are formed from degenerated eosinophils seen in asthmatic. Curchmann's spirals are coiled basophilic mucinous fibrils seen also in asthmatics.
Foreign Bodies:
Foreign bodies are seen in coughed up sputum due to aspiration of food and drinks. Vegetable matter is often removed by bronchoscopy. Two groups are most susceptible to aspiration - young children and nursing home patients with bulbar palsy, stroke with dysphagia, and neurogenerative diseases. Uncommon objects found in the sputum are - broken toy pieces, magnets, glass beads, buttons, pennies, pins, small nails, partial dentures, small fruit seeds, decayed teeth, surgical sutures, hard candies, and others.
Distinctive features of Cystic fibrosis sputum are very sticky green fruity in smell. In the case of bronchiectasis, the collected sputum separates into three layers, the bottom layer is the necrotic tissues, the clear middle layer and the top foamy layer.
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