Sputum Culture

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[lwptoc] Sputum culture is the most common test to detect and determine respiratory tract disease caused by fungi or bacteria. It helps in diagnosing pneumonia, bronchitis, tuberculosis, cancer, bronchiectasis, and lung gangrene. In the case of bronchitis and other inflammatory diseases, it is necessary to take a general sputum test. Typically, one can collect sputum… Read More

Sputum Culture


Sputum culture is the most common test to detect and determine respiratory tract disease caused by fungi or bacteria. It helps in diagnosing pneumonia, bronchitis, tuberculosis, cancer, bronchiectasis, and lung gangrene. In the case of bronchitis and other inflammatory diseases, it is necessary to take a general sputum test. Typically, one can collect sputum by coughing up or aspirating from the trachea.

What is sputum?

Sputum is a combination of saliva and mucus, coughed up from the lower respiratory tract (trachea and bronchi) during expectoration. Coughing up sputum mostly occurs during infectious and inflammatory conditions of the upper and lower respiratory tract.

In a healthy person, sputum is in liquid, transparent, and odorless form. It contains more than 95% of water, 5% proteins, carbohydrates, and mineral salts. In patients with respiratory diseases, sputum may contain protein, blood, polysaccharide components, bacteria, and viruses. Therefore, a sputum sample is crucial for the diagnosis of respiratory diseases.

Why is sputum culture necessary?

Microscopic examination of sputum helps to identify the cause of disease of the lungs and other respiratory organs. It also helps to obtain all the necessary information about the provoking conditions. The color and consistency of sputum may vary depending on the disease. Based on the data obtained, the doctor determines the disease causative agent and selects the best treatment regimen. The test sometimes helps to detect the cancerous cells in the lung. Additional diagnosis is a must for the same.

Cough is often the first symptom of diseases such as tuberculosis and bronchial adenoma. X-ray signs appear later, and bronchoscopy is not always an affordable examination. Correctly collected sputum is a simple, cost-effective, and informative method for early diagnosis. Therefore, if a doctor prescribes this examination, it is necessary not just to “spit into a container” but to take quality sputum for analysis.

When to do a sputum culture?

The sputum culture is a test used extensively in medicine since it is convenient to do it; it’s affordable and can provide a lot of useful information. The information it provides helps to identify the exact cause of respiratory infection. 

Sputum culture for general analysis is necessary for those patients who have a suspicion of chronic or acute diseases of the respiratory system like:

  • Pneumonia, Bronchial asthma, Bronchiectasis, Bronchitis, Tuberculosis, and Chronic obstructive pulmonary disease
  • Neoplasms of the respiratory system, fungal infection of the lungs, and interstitial lung diseases
  • If you have a cough with sputum (lasting more than 2-3 weeks)

How to do a sputum culture?

Preparing for analysis

While preparing for analysis, you need to follow some guidelines for an accurate result. To provide a quality sample, the patient must adhere to the following recommendations before collecting sputum:

  • Drinking plenty of warm water
  • Taking expectorants
  • Brushing teeth and rinsing your mouth before the procedure

Taking sputum samples

  • It is best to collect sputum samples in the early morning. It should be gradually coughing up and not forceful coughing. 
  • Before coughing up mucus, take three slow breaths in and out, holding your breath between them for 5 seconds.
  • Cough up and spit the accumulated phlegm into a jar
  • Make sure that while expectorating, no saliva from the oral cavity has entered the jar.
  • Repeat all the above steps until the sample level reaches the 5 ml mark.
  • Once you collect sputum, carry it to the laboratory for analysis. Make sure you deliver it within two hours as per doctors advice. 
  • Do not touch collected sputum with fingers, and the jar should be tightly closed with a lid immediately. 
  • If there is a suspicion of infectious disease, wash your hands after collecting the samples.

How to collect the sputum for tuberculosis

A cough that does not stop for more than three weeks is a sign of prolonged disease like tuberculosis, which needs sputum testing. Tuberculosis is a severe infectious disease that needs accurate diagnosis, so pathogenic mucus is collected only under the doctor’s advice and supervision. You can collect a sample at home or outpatient. If you suspect tuberculosis, you have to give sputum three times. The first early in the morning, the second – after four hours, and the last – the next day. 

It is necessary to collect the sputum for tuberculosis in a separate room, with a normally functioning ventilation system or open windows in the absence of other people living together. Such precautions are necessary since tuberculosis is a contagious infection that spreads through respiratory droplets while coughing or sneezing. It can pose a danger to healthy family members.

How to get a sputum test if there is no cough?

It will be tough to collect sputum if there is a dry cough or no cough at all. Here is what you can do:-

  • Consume plenty of fluids one day before a test. 
  • Taking expectorant for thinning and loosening mucus (Doctor’s consult is a must)
  • Postural drainage:- It helps you to drain mucus from the lung by changing position towards gravity. Additionally, it is useful for treating various respiratory diseases such as bronchiectasis, cystic fibrosis, and pneumonia. The postural drainage technique is short and easy to perform. You need to lie down on a flat hard surface and place a pillow under your stomach. You can also take several positions per session (on the side, lying on your stomach, or back). Pregnant women should exclude the position on the stomach.

Sputum sample through bronchoscopy

  • Bronchoscopy is a diagnostic procedure that helps to examine the larynx, trachea, and bronchi. It involves pushing a bronchoscope through the oral cavity into the airway – a flexible or rigid probe with a camera at the end. As the device moves, the doctor assesses the conditions of various parts of the respiratory tract. If necessary, he takes a sputum or biopsy sample for further analysis.

Advantages and disadvantages of sputum culture

The positive aspects of sputum culture include:

  • Fewer chances of a false result.
  • Easy to perform, doesn’t require any special diet to follow.
  • Based on the analysis, it makes it easy for a doctor to prescribe the treatment regimen correctly.

Disadvantages include:

  • You may need to wait quite a long time to get a result.
  • You have to make sure to get quality sputum.

Sputum culture result

A healthy person does not produce sputum. Sputum is an irregular discharge from the respiratory tract that comes off when you cough. To get a result of your sputum test, you may need to wait for up to three days.

Here are the possible results of the sputum analysis:

  • If sputum is transparent and thick- it is a sign of viral infection of the respiratory tract. It is also common in acute bronchitis and acute respiratory viral infection (ARVI).
  • Blood in sputum (hemoptysis) indicates upper respiratory infections, lung cancer, tuberculosis, or asthma.
  • Cloudy sputum, yellow-green, white, or containing pus is a sign of lung abscess, pneumonia, bronchial asthma, or chronic obstructive bronchitis. Purulent sputum can also be a sign of ENT conditions(sinusitis, rhinitis).
  • The presence of neutrophilic leukocytes (over 25 cells) indicates respiratory tract infection.
  • The presence of high levels of eosinophils (over 50–90%) indicates a parasitic infection that can affect your immune system.
  • The presence of a curschmann’s spirals and Charcot–Leyden crystals in sputum can be a reason for bronchial asthma.

Severe coughing is a sign of respiratory tract disease that often occurs with the expectoration of mucus. Sputum analysis is a simple and effective method to detect the disease. It provides the most critical information about the condition; its severity; and helps to choose the right treatment regimen.