White／yellow／yellow-green／gray-green, understand the clinical significance of sputum color after reading it!

Sputum is the secretion produced by trachea, bronchus and alveoli. Under normal circumstances, the amount of secretion is small, and under pathological conditions, such as lung inflammation, tuberculosis and tumor, the amount of sputum increases, and its properties and composition change. Clinically, sputum specimens are often used to identify the pathogenic bacteria that cause infection, so as to make a correct etiological diagnosis and choose effective antibiotics.

When we operate the airway clearance technology for patients with sputum retention, patients can often cough up sputum with various properties and colors. What do these properties and colors represent? I believe many colleagues have the same doubts as me. This paper has inquired about some information and made some simple introductions.

First, the mechanism and classification of sputum color.　

1.1 The mechanism of sputum color …　

Robertson discovered in 1955 that the color of green sputum was caused by myeloperoxidase. When inflammation occurs, the eosinophil blue granules in neutrophils and monocytes contain green myeloperoxidase, so when the amount of neutrophils and monocytes in secretions increases, sputum with purulent nature during infection appears.

In addition, Pseudomonas aeruginosa can also produce a variety of pigments, including pyocyanin, pyocyanin, pyocyanin and fluorescein. Thereby causing the color of sputum to become darker.

1.2 Classification of sputum color　

Bronkotest5-point chart is a standardized method for sputum color classification, in which 1-2 is white to light yellow, and 3,4 and 5 are more and more purulent. Green indicates a bacterial infection. In AECOPD population, the positive predictive value of the presence of green sputum for bacterial infection is 80%, while the negative predictive value of no green sputum is 93%.

Second, the meaning of the nature and color of sputum.　

2.1 the nature of sputum　

It can be divided into mucinous, serous, purulent and bloody.

Mucinous sputum is more common in the early stage of acute bronchitis, bronchial asthma and lobar pneumonia, and can also be seen in chronic bronchitis and tuberculosis.

Serous sputum is found in pulmonary edema, alveolar cell carcinoma, etc.

Purulent sputum is common in purulent bacterial lower respiratory tract infections, such as pneumonia, bronchiectasis and lung abscess.

Bloody phlegm is caused by the invasion of respiratory mucosa, damage to capillaries or blood infiltration into human alveoli.

2.2 Color and smell of phlegm　

Rusty sputum is the characteristic of typical pneumococcal pneumonia. (The picture comes from Zhou Tingyin-Clinical Microbiological Diagnosis and Diagram)　　

Yellow-green or emerald-green sputum suggests Pseudomonas aeruginosa infection; (The picture comes from Zhou Tingyin-Clinical Microbiological Diagnosis and Diagram)　　

Staphylococcus aureus infection is suggested by golden yellow sputum. (The picture comes from Zhou Tingyin-Clinical Microbiological Diagnosis and Diagram)　　

The phlegm is white, thick and silky, suggesting fungal infection;　

A large number of thin serous sputum containing dermoid suggests echinococcosis (echinococcosis);

Pink foam sputum is the characteristic of pulmonary edema;

Odor sputum suggests anaerobic infection.

Third, the application of sputum color in different diseases　

3.1 Diagnostic value of bacterial infection in patients with acute cough　

In the study of sputum samples obtained from 241 patients with acute cough during medical treatment. Bacterial infection was confirmed in 28 samples (12%), and typical pathogens were isolated, such as Streptococcus pneumoniae (n=9), Haemophilus influenzae (n=5), haemophilus parainfluenzae (n=5) and Moraxella catarrhalis (n=4).

The results showed that bacterial infection was obviously more common in yellow or green sputum samples.

3.2 Application in non-cystic fibrosis bronchiectasis.　

In a study on the relationship between sputum color of patients with bronchiectasis and bacterial colonization, 141 stable sputum samples of patients with bronchiectasis were graded by color chart.

The results showed that the coincidence rate was 80.9% in mucus group, 90.3% in mucus suppuration group and 76.3% in suppuration group. That is, phlegm and pus are related to bacterial colonization. Haemophilus influenzae, Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus pneumoniae, etc. are common colonization bacteria of metaphase suppuration, so the color of sputum can be used as a useful aid for clinical management while waiting for the formal results of sputum microbiology.

3.3 application in AECOPD patients·　

The report of Global Obstructive Pneumonia Initiative (GOLD) in 2022 emphasized that sputum color during AECOPD was highly sensitive and specific to high bacterial load aggregation. In a systematic review on the existence of sputum color as bacteria in patients with acute exacerbation of chronic obstructive pulmonary disease, this systematic review and meta-analysis show that there is moderate evidence that purulent sputum defined by yellow or green during the exacerbation of chronic obstructive pulmonary disease is related to the significant increase of potential pathogens, which supports the GOLD report. However, there is still a lack of high-quality evidence to support the use of sputum color as a diagnostic pathogen in AECOPD.

Summary　

The change of sputum color in the process of disease aggravation is a sensitive and specific marker of pathogen existence, which can predict the number of high pathogens in bronchial secretions. But it can’t distinguish between virus and bacterial infection. Therefore, it should not be used to decide the choice of treatment, especially whether to use antibiotics.

Reference materials　

[1] Ge Junbo, Xu Yongjian, Wang Chen. Internal Medicine [M]. 9th edition. Beijing: People’s Medical Publishing House, 2018.

[2] Wan Yonghong, Lu Xuefeng. Diagnostics [M]. 9th edition. Beijing: People’s Health Publishing House, 2018.

[3]Channa S, Gale N, Lai E, Hall L, Quinn M, Turner AM. Colour vision deficiency and sputum colour charts in COPD patients: an exploratory mixed-method study. NPJ Prim Care Respir Med. 2021; 31(1):13. Published 2021 Mar 4. doi:10.1038/s41 533- 021- 00225-z

[4]Altiner A, Wilm S, Däubener W, et al. Sputum colour for diagnosis of a bacterial infection in patients with acute cough. Scand J Prim Health Care. 2009; 27(2):70-73. doi:10.1080/02813430902759663

[5]Murray MP, Pentland JL, Turnbull K, MacQuarrie S, Hill AT. Sputum colour: a useful clinical tool in non-cystic fibrosis bronchiectasis. Eur Respir J. 2009; 34(2):361-364. doi:10.1183/09031936.00163208

[6]Sputum colour and bacteria in chronic bronchitis exacerbations: a pooled analysis

Vollenweider DJ, Frei A, Steurer-Stey CA, Garcia-Aymerich J, Puhan MA. Antibiotics for exacerbations of chronic obstructive pulmonary disease. Cochrane Database Syst Rev. 2018; 10(10):CD010257. Published 2018 Oct 29. doi:10.1002/14651858.CD010257.pub2

[7]Spies R, Potter M, Hollamby R, et al. Sputum colour as a marker for bacteria in acute exacerbations of COPD: protocol for a systematic review and meta-analysis. Syst Rev. 2021; 10(1):211. Published 2021 Jul 27. doi:10.1186/s13643-021-01767-6

[8]Chen K, Pleasants KA, Pleasants RA, et al. A Systematic Review and Meta-Analysis of Sputum Purulence to Predict Bacterial Infection in COPD Exacerbations. COPD. 2020; 17(3):311-317. doi:10.1080/15412555.2020.1766433

[9]Vollenweider DJ, Frei A, Steurer-Stey CA, Garcia-Aymerich J, Puhan MA. Antibiotics for exacerbations of chronic obstructive pulmonary disease. Cochrane Database Syst Rev. 2018 Oct 29; 10(10):CD010257. doi: 10.1002/14651858.CD010257.pub2. PMID: 30371937; PMCID: PMC6517133.