Health Guide

Microbial culture of sputum

What is this test?

This test detects and identifies bacteria from a culture of sputum. This test is used to help diagnose possible bacterial causes of respiratory tract infections[1] such as community acquired pneumonia[2][3][4][5][6].

What are related tests?

Why do I need this test?

Laboratory tests may be done for many reasons. Tests are performed for routine health screenings or if a disease or toxicity is suspected. Lab tests may be used to determine if a medical condition is improving or worsening. Lab tests may also be used to measure the success or failure of a medication or treatment plan. Lab tests may be ordered for professional or legal reasons. You may need this test if you have:

  • Acute chest syndrome
  • Acute exacerbation of pulmonary cystic fibrosis
  • Aspiration pneumonitis
  • Community acquired pneumonia
  • Pneumonic plague

When and how often should I have this test?

When and how often laboratory tests are done may depend on many factors. The timing of laboratory tests may rely on the results or completion of other tests, procedures, or treatments. Lab tests may be performed immediately in an emergency, or tests may be delayed as a condition is treated or monitored. A test may be suggested or become necessary when certain signs or symptoms appear.

Due to changes in the way your body naturally functions through the course of a day, lab tests may need to be performed at a certain time of day. If you have prepared for a test by changing your food or fluid intake, lab tests may be timed in accordance with those changes. Timing of tests may be based on increased and decreased levels of medications, drugs or other substances in the body.

The age or gender of the person being tested may affect when and how often a lab test is required. Chronic or progressive conditions may need ongoing monitoring through the use of lab tests. Conditions that worsen and improve may also need frequent monitoring. Certain tests may be repeated to obtain a series of results, or tests may need to be repeated to confirm or disprove results. Timing and frequency of lab tests may vary if they are performed for professional or legal reasons.

You will need to provide an early morning sputum sample for this test[7].

How should I get ready for the test?

Before a sputum sample is collected, you may be asked to drink more fluids. Drinking more fluids may help you produce a sputum sample.

For this test, a sputum sample is obtained before taking an antibiotic[2][3]. Tell your healthcare worker if you are taking any medications at the time of the test.

How is the test done?

Sputum is mucus that is secreted by the airways and lungs. To collect a sample of sputum, you may be asked to cough forcefully, and spit out sputum into a container. If you are unable to produce a sputum sample, you may need to have the sample induced. To induce a sputum sample, a healthcare worker will prepare a solution in a nebulizer for you to inhale. You will be asked to inhale the solution over a period of time, which may last up to 20 minutes. You will then be asked to cough and spit out sputum into a container.

How will the test feel?

The amount of discomfort you feel will depend on many factors, including your sensitivity to pain. Communicate how you are feeling with the person doing the test. Inform the person doing the test if you feel that you cannot continue with the test.

Generally, collection of a sputum sample is not painful. If the sample is induced, the coughing may be uncomfortable.

What should I do after the test?

After a sputum sample is collected, call the healthcare worker if you experience a new onset of pain in your throat, trouble swallowing, or if you are coughing up blood.

What are the risks?

Sputum: If you are unable to produce a sputum sample on your own, it may need to be induced. Risks with collection of an induced sputum cell sample include minor damage to the throat and trachea. The person doing this test may need to perform it more than once. Talk to your healthcare worker if you have any concerns about the risks of giving a sputum sample.

What are normal results for this test?

Laboratory test results may vary depending on your age, gender, health history, the method used for the test, and many other factors. If your results are different from the results suggested below, this may not mean that you have a disease. Contact your healthcare worker if you have any questions. The following is considered to be a normal result for this test:

Adults and Children: Negative

What follow up should I do after this test?

Ask your healthcare worker how you will be informed of the test results. You may be asked to call for results, schedule an appointment to discuss results, or notified of results by mail. Follow up care varies depending on many factors related to your test. Sometimes there is no follow up after you have been notified of test results. At other times follow up may be suggested or necessary. Some examples of follow up care include changes to medication or treatment plans, referral to a specialist, more or less frequent monitoring, and additional tests or procedures. Talk with your healthcare worker about any concerns or questions you have regarding follow up care or instructions.

Where can I get more information?

Related Companies

  • American Lung Association -
  • Centers for Disease Control and Prevention -


[1] Tietz NW (Ed): Clinical Guide to Laboratory Tests, 3rd ed. W. B. Saunders, Philadelphia, PA, 1995.

[2] Garcia-Vazquez E, Marcos MA, Mensa J, et al: Assessment of the usefulness of sputum culture for diagnosis of community-acquired pneumonia using the PORT predictive scoring system. Arch Intern Med 2004; 164(16):1807-1811.

[3] Mandell LA, Bartlett JG, Dowell SF, et al: Update of practice guidelines for the management of community-acquired pneumonia in immunocompetent adults. Infectious Diseases Society of America (IDSA).. Clin Infect Dis 2003; 37:1405-1433.

[4] Cunha BA: Community-acquired pneumonia. Diagnostic and therapeutic approach. Med Clin North Am 2001; 85(1):43-77.

[5] Whitby M, Kristinsson KG, & Brown M: Assessment of rapid methods of pneumococcal antigen detection in routine sputum bacteriology. J Clin Pathol 1985; 38(3):341-344.

[6] Tebbutt GM & Coleman DJ: Evaluation of some methods for the laboratory examination of sputum. J Clin Pathol 1978; 31(8):724-729.

[7] Henry JB: Clinical Diagnosis and Management by Laboratory Methods, 20th ed. Saunders, 2001.

Last Updated: 7/4/2018
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