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Abnormal sputum
Enterococcus histological pneumonia 01.png
Cocci-shaped Enterococcus sp. bacteria taken from a pneumonia patient.
  • /'spju.təm/
Specialty Pulmonology

Sputum is mucus and is the name used for the coughed-up material (phlegm) from the lower airways (trachea and bronchi). In medicine, sputum samples are usually used for naked eye exam, microbiological investigations of respiratory infections, and cytological investigations of respiratory systems. It is critical that the patient not give a specimen that includes any mucoid material from the interior of the nose. Naked eye exam of sputum can be done at home by a patient in order to note the various colors (see below). Any hint of yellow color suggests an airway infection (but does not indicate between the types of organisms causing it). Such color hints are best detected when the sputum is viewed on a very white background such as white paper, a white pot, or a white sink surface. The more intense the yellow color, the more likely it is a bacterial infection (bronchitis, bronchopneumonia, or pneumonia).

Mucus slippery secretion produced by, and covering, mucous membranes

Mucus is a polymer. It is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It is a viscous colloid containing inorganic salts, antiseptic enzymes, immunoglobulins, and glycoproteins such as lactoferrin and mucins, which are produced by goblet cells in the mucous membranes and submucosal glands. Mucus serves to protect epithelial cells in the respiratory, gastrointestinal, urogenital, visual, and auditory systems; the epidermis in amphibians; and the gills in fish, against infectious agents such as fungi, bacteria and viruses. Most of the mucus produced is in the gastrointestinal tract.

Phlegm is a liquid secreted by the mucous membranes of mammals. Its definition is limited to the mucus produced by the respiratory system, excluding that from the nasal passages, and particularly that which is expelled by coughing (sputum). Phlegm is in essence a water-based gel consisting of glycoproteins, immunoglobulins, lipids and other substances. Its composition varies depending on climate, genetics, and state of the immune system. Its color can vary from transparent to pale or dark yellow and green, from light to dark brown, and even to dark grey depending on the constituents.


Cytopathology is a branch of pathology that studies and diagnoses diseases on the cellular level. The discipline was founded by George Nicolas Papanicolaou in 1928. Cytopathology is generally used on samples of free cells or tissue fragments, in contrast to histopathology, which studies whole tissues.



The best sputum samples contain very little saliva, [1] as saliva contaminates the sample with oral bacteria. This is especially true for samples for lab testing in cytology or microbiology. Specimen adequacy is assessed by the laboratory technologists by examining a Gram stain or cytology stain of the sputum. More than 25 squamous epithelial cells at low power magnification exam with the microscope strongly suggests salivary contamination. [2] Sputum samples have been used to quantify the degree of airway inflammation in human diseases such as asthma. Specifically, this work has demonstrated that sub group of severe asthma patients have airway inflammation that is resistant to treatment with corticosteroids. [3]

Saliva is a fluid substance formed in the mouths of animals, secreted by the salivary glands. Human saliva comprises 99.5⁠% water plus electrolytes, mucus, white blood cells, epithelial cells, enzymes, antimicrobial agents such as secretory IgA and lysozyme.

Bacteria A domain of prokaryotes – single celled organisms without a nucleus

Bacteria are a type of biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep portions of Earth's crust. Bacteria also live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, and only about half of the bacterial phyla have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology.

Microbiology study of microscopic organisms

Microbiology is the study of microorganisms, those being unicellular, multicellular, or acellular. Microbiology encompasses numerous sub-disciplines including virology, parasitology, mycology and bacteriology.

When a sputum specimen is plated out in microbiology, it is best to get the portion of the sample that most looks like yellow pus onto the swab. If there is any blood in the sputum, this should also be on the swab.[ citation needed ] Microbiological sputum samples are used to look for infections, such as Moraxella catarrhalis , Mycobacterium tuberculosis , Streptococcus pneumoniae , and Haemophilus influenzae . Other pathogens can also be found.

Moraxella catarrhalis is a fastidious, nonmotile, Gram-negative, aerobic, oxidase-positive diplococcus that can cause infections of the respiratory system, middle ear, eye, central nervous system, and joints of humans. It causes the infection of the host cell by sticking to the host cell using trimeric autotransporter adhesins.

<i>Mycobacterium tuberculosis</i> Species of bacterium

Mycobacterium tuberculosis is a species of pathogenic bacteria in the family Mycobacteriaceae and the causative agent of tuberculosis. First discovered in 1882 by Robert Koch, M. tuberculosis has an unusual, waxy coating on its cell surface primarily due to the presence of mycolic acid. This coating makes the cells impervious to Gram staining, and as a result, M. tuberculosis can appear either Gram-negative or Gram-positive. Acid-fast stains such as Ziehl-Neelsen, or fluorescent stains such as auramine are used instead to identify M. tuberculosis with a microscope. The physiology of M. tuberculosis is highly aerobic and requires high levels of oxygen. Primarily a pathogen of the mammalian respiratory system, it infects the lungs. The most frequently used diagnostic methods for tuberculosis are the tuberculin skin test, acid-fast stain, culture, and polymerase chain reaction.

Purulent sputum [4] contains pus, composed of white blood cells, cellular debris, dead tissue, serous fluid, and viscous liquid (mucus). Purulent sputum is typically yellow or green. It is seen in cases of bronchiectasis, lung abscess, an advanced stage of bronchitis, or acute upper respiratory tract infection (common cold, laryngitis).


Pus is an exudate, typically white-yellow, yellow, or yellow-brown, formed at the site of inflammation during bacterial or fungal infection. An accumulation of pus in an enclosed tissue space is known as an abscess, whereas a visible collection of pus within or beneath the epidermis is known as a pustule, pimple, or spot.

In physiology, the term serous fluid or serosal fluid is any of various body fluids resembling serum, that are typically pale yellow and transparent and of a benign nature. The fluid fills the inside of body cavities. Serous fluid originates from serous glands, with secretions enriched with proteins and water. Serous fluid may also originate from mixed glands, which contain both mucous and serous cells. A common trait of serous fluids is their role in assisting digestion, excretion, and respiration.

Bronchiectasis congenital disorder of respiratory system

Bronchiectasis is a disease in which there is permanent enlargement of parts of the airways of the lung. Symptoms typically include a chronic cough with mucus production. Other symptoms include shortness of breath, coughing up blood, and chest pain. Wheezing and nail clubbing may also occur. Those with the disease often get frequent lung infections.


Sputum can be (when examined by the naked eye):[ citation needed ]

  1. Bloody [4] (hemoptysis)
    1. Blood-streaked sputum – inflammation of throat (larynx and/or trachea) or bronchi; lung cancer; other bleeding erosions, ulcers, or tumors of the lower airway.
    2. Pink sputum – sputum evenly mixed with blood from alveoli and/or small peripheral bronchi.
    3. Massive blood – cavitary tuberculosis or tumor such as lung cancer of lung, or lung abscess; bronchiectasis; lung infarction; pulmonary embolism.
  2. Green or greenish colored - indicative of longstanding respiratory infection (green from degenerative changes in cell debris) as in pneumonia, ruptured lung abscess, chronic infectious bronchitis, and infected bronchiectasis or cystic fibrosis.
  3. Rust colored – usually caused by pneumococcal bacteria (in pneumonia), pulmonary embolism, lung cancer or pulmonary tuberculosis.
  4. Brownish – chronic bronchitis (greenish/yellowish/brown); chronic pneumonia (whitish-brown); tuberculosis; lung cancer.
  5. Yellow, yellowish purulent – containing pus. "The sputum color of patients with acute cough and no underlying chronic lung disease does not imply therapeutic consequences such as prescription of antibiotics." [5] The color can provide hints as to effective treatment in chronic bronchitis patients: [6]
    1. A yellow-greenish (mucopurulent) color suggests that treatment with antibiotics can reduce symptoms. The green color is caused by degenerating neutrophil verdoperoxidase.
  6. Whitish gray sputum color against a white color background (such as a white sink surface) tends to indicate either a specimen from someone who is dehydrated, and/or from an older person, and/or a specimen with a mixed, modest number of eosinophils and maybe some acute inflammatory neutrophil cells (this last choice tends to suggest a chronic allergic bronchitis).
  7. A white, milky, or opaque (mucoid) appearance means that antibiotics are less likely to be effective in treatment because the likelihood is greater of a viral infection or allergy (even asthma...thick sputum) than of antibiotic-responsive micro-organisms.
  8. Foamy white – may come from earlier-phase pulmonary edema.
  9. Frothy pink – may indicate more severe pulmonary edema. Antibiotics may not be necessary at this time.
  10. Clear – pulmonary embolism (clear to frothy); COPD chronic obstructive pulmonary disease (clear to gray); viral respiratory infection (clear to whitish & sometimes a hint of yellow); asthma (thick and white to yellowish).

See also

Related Research Articles

Cough medical symptom, reflex to clear large breathing passages

A cough is a sudden, and often repetitively occurring, protective reflex which helps to clear the large breathing passages from fluids, irritants, foreign particles and microbes. The cough reflex consists of three phases: an inhalation, a forced exhalation against a closed glottis, and a violent release of air from the lungs following opening of the glottis, usually accompanied by a distinctive sound.

Hemoptysis is the coughing up of blood or blood-stained mucus from the bronchi, larynx, trachea, or lungs. This can occur with lung cancer, infections such as tuberculosis, bronchitis, or pneumonia, and certain cardiovascular conditions. Hemoptysis is considered massive at 300 mL. In such cases, there are always severe injuries. The primary danger comes from choking, rather than blood loss.

Respiratory tract Organs involved in transmission of air to and from the point where gases diffuse into tissue

In humans, the respiratory tract is the part of the anatomy of the respiratory system involved with the process of respiration. Air is breathed in through the nose or the mouth. In the nasal cavity, a layer of mucous membrane acts as a filter and traps pollutants and other harmful substances found in the air. Next, air moves into the pharynx, a passage that contains the intersection between the esophagus and the larynx. The opening of the larynx has a special flap of cartilage, the epiglottis, that opens to allow air to pass through but closes to prevent food from moving into the airway.

Acute bronchitis short-term inflammation of the bronchi (large and medium-sized airways) of the lungs

Acute bronchitis, also known as a chest cold, is short-term inflammation of the bronchi of the lungs. The most common symptom is a cough. Other symptoms include coughing up mucus, wheezing, shortness of breath, fever, and chest discomfort. The infection may last from a few to ten days. The cough may persist for several weeks afterward with the total duration of symptoms usually around three weeks. Some have symptoms for up to six weeks.

Bronchus airway in the respiratory tracti

A bronchus is a passage of airway in the respiratory system that conducts air into the lungs. The first bronchi to branch from the trachea are the right main bronchus and the left main bronchus. These are the widest and enter the lungs at each hilum, where they branch into narrower secondary bronchi known as lobar bronchi, and these branch into narrower tertiary bronchi known as segmental bronchi. Further divisions of the segmental bronchi are known as 4th order, 5th order, and 6th order segmental bronchi, or grouped together as subsegmental bronchi. The bronchi when too narrow to be supported by cartilage are known as bronchioles. No gas exchange takes place in the bronchi.

Lower respiratory tract infection

Lower respiratory tract infection (LRTI), while often used as a synonym for pneumonia, can also be applied to other types of infection including lung abscess and acute bronchitis. Symptoms include shortness of breath, weakness, fever, coughing and fatigue.

Atelectasis collapse or closure of a lung resulting in reduced or absent gas exchange

Atelectasis is the collapse or closure of a lung resulting in reduced or absent gas exchange. It may affect part or all of a lung. It is usually unilateral. It is a condition where the alveoli are deflated down to little or no volume, as distinct from pulmonary consolidation, in which they are filled with liquid. It is often called a collapsed lung, although that term may also refer to pneumothorax.

Lung abscess lung disease characterized by microbial infection which causes a type of liquefactive necrosis of the pulmonary tissue and formation of cavities containing necrotic debris or fluid

Lung abscess is a type of liquefactive necrosis of the lung tissue and formation of cavities containing necrotic debris or fluid caused by microbial infection.

Respiratory disease disease of the respiratory system

Respiratory disease is a medical term that encompasses pathological conditions affecting the organs and tissues that make gas exchange difficult in higher organisms, and includes conditions of the upper respiratory tract, trachea, bronchi, bronchioles, alveoli, pleura and pleural cavity, and the nerves and muscles of breathing. Respiratory diseases range from mild and self-limiting, such as the common cold, to life-threatening entities like bacterial pneumonia, pulmonary embolism, acute asthma and lung cancer.

Lobar pneumonia

Lobar pneumonia is a form of pneumonia characterized by inflammatory exudate within the intra-alveolar space resulting in consolidation that affects a large and continuous area of the lobe of a lung.

A sputum culture is a test to detect and identify bacteria or fungi that infect the lungs or breathing passages. Sputum is a thick fluid produced in the lungs and in the adjacent airways. Normally, fresh morning sample is preferred for the bacteriological examination of sputum. A sample of sputum is collected in a sterile, wide-mouthed, dry, leak-proof and break-resistant plastic-container and sent to the laboratory for testing. Sampling may be performed by sputum being expectorated, induced, or taken via an endotracheal tube with a protected specimen brush in an intensive care setting. For selected organisms such as Cytomegalovirus or "Pneumocystis jiroveci" in specific clinical settings a bronchoalveolar lavage might be taken by an experienced pneumologist. If no bacteria or fungi grow, the culture is negative. If organisms that can cause the infection grow, the culture is positive. The type of bacterium or fungus is identified by microscopy, colony morphology and biochemical tests of bacterial growth.

Bronchitis type of lower respiratory disease

Bronchitis is an inflammation of the bronchi in the lungs. Symptoms include coughing up mucus, wheezing, shortness of breath, and chest discomfort. Bronchitis is divided into two types: acute and chronic. Acute bronchitis is also known as a chest cold.

Obstructive lung disease

Obstructive lung disease is a category of respiratory disease characterized by airway obstruction. Many obstructive diseases of the lung result from narrowing (obstruction) of the smaller bronchi and larger bronchioles, often because of excessive contraction of the smooth muscle itself. It is generally characterized by inflamed and easily collapsible airways, obstruction to airflow, problems exhaling and frequent medical clinic visits and hospitalizations. Types of obstructive lung disease include; asthma, bronchiectasis, bronchitis and chronic obstructive pulmonary disease (COPD). Although COPD shares similar characteristics with all other obstructive lung diseases, such as the signs of coughing and wheezing, they are distinct conditions in terms of disease onset, frequency of symptoms and reversibility of airway obstruction. Cystic fibrosis is also sometimes included in obstructive pulmonary disease.

Geotrichosis opportunistic mycosis that has material basis in Galactomyces geotrichum, results in systemic infection in immunocompromised people

Geotrichosis is a mycosis caused by Geotrichum candidum.

Acute exacerbation of chronic obstructive pulmonary disease

Acute exacerbation of COPD is a sudden worsening of COPD symptoms that typically lasts for several days. It may be triggered by an infection with bacteria or viruses or by environmental pollutants. Typically, infections cause 75% or more of the exacerbations; bacteria can roughly be found in 25% of cases, viruses in another 25%, and both viruses and bacteria in another 25%. Airway inflammation is increased during the exacerbation resulting in increased hyperinflation, reduced expiratory air flow and decreased gas exchange.

Eosinophilic bronchitis

Eosinophilic bronchitis (EB) is a type of airway inflammation due to excessive mast cell recruitment and activation in the superficial airways as opposed to the smooth muscles of the airways as seen in asthma. It often results in a chronic cough. Lung function tests are usually normal. Inhaled corticosteroids are often an effective treatment.

Chronic Mycoplasma pneumonia and Chlamydia pneumonia infections are associated with the onset and exacerbation of asthma. These microbial infections result in chronic lower airway inflammation, impaired mucociliary clearance, an increase in mucous production and eventually asthma. Furthermore, children who experience severe viral respiratory infections early in life have a high possibility of having asthma later in their childhood. These viral respiratory infections are mostly caused by respiratory syncytial virus (RSV) and human rhinovirus (HRV). Although RSV infections increase the risk of asthma in early childhood, the association between asthma and RSV decreases with increasing age. HRV on the other hand is an important cause of bronchiolitis and is strongly associated with asthma development. In children and adults with established asthma, viral upper respiratory tract infections (URIs), especially HRVs infections, can produce acute exacerbations of asthma. Thus, Chlamydia pneumoniae, Mycoplasma pneumoniae and human rhinoviruses are microbes that play a major role in non-atopic asthma.

Chronic cough is long-term coughing, sometimes defined as more than several weeks or months. The term can be used to describe the different causes related to coughing, the 3 main ones being; upper airway cough syndrome, asthma and gastroesophageal reflux disease. It occurs in the upper airway of the respiratory system. Generally, a cough lasts around 1–2 weeks, however, chronic cough can persist for an extended period of time defined as 6 weeks or longer. People with chronic cough often experience more than one cause present. Due to the nature of the syndrome the treatments that are used are similar however there is a subsequent number of treatments available.


  1. Clinical Microbiology procedures handbook, American Society for Microbiology 2nd Ed. 2007 update
  2. Gershman, Neil H.; Liu, Hong; Wong, Hofer H.; Liu, Jane T.; Fahy, John V. (August 1999). "Fractional analysis of sequential induced sputum samples during sputum induction: Evidence that different lung compartments are sampled at different time points". Journal of Allergy and Clinical Immunology. 104 (2): 322–328. doi:10.1016/S0091-6749(99)70374-X.
  3. Peters, Michael C.; Kerr, Sheena; Dunican, Eleanor M.; Woodruff, Prescott G.; Fajt, Merritt L.; Levy, Bruce D.; Israel, Elliot; Phillips, Brenda R.; Mauger, David T.; Comhair, Suzy A.; Erzurum, Serpil C.; Johansson, Mats W.; Jarjour, Nizar N.; Coverstone, Andrea M.; Castro, Mario; Hastie, Annette T.; Bleecker, Eugene R.; Wenzel, Sally E.; Fahy, John V. (March 2018). "Refractory airway type 2 inflammation in a large subgroup of asthmatic patients treated with inhaled corticosteroids". Journal of Allergy and Clinical Immunology. doi:10.1016/j.jaci.2017.12.1009.
  4. 1 2 Richard F. LeBlond; Richard L. DeGowin; Donald E. Brown (2004). DeGowin's diagnostic examination. New York: McGraw-Hill. ISBN   0-07-140923-8.
  5. Altiner A, Wilm S, Däubener W, Bormann C, Pentzek M, Abholz HH, Scherer M (2009). "Sputum color for diagnosis of a bacterial infection in patients with acute cough". Scand J Prim Health Care. 27 (2): 70–3. doi:10.1080/02813430902759663. PMC   3410464 . PMID   19242860.
  6. Sputum Color is the Key to Treating Acute COPD Exacerbations