How the Test is Performed

A health care provider will often collect sputum samples in the morning. The doctor or nurse may have you rinse your mouth first. The goal is to bring sputum up from deeper in your airways and your throat.

You will be asked to take three deep breaths, then force up some sputum amount by coughing deeply. You will spit any sputum that comes up into a sterile cup. The sputum is then taken to the laboratory. There, it is placed in a special substance (medium) under conditions that allow the bacteria or fungi to grow.

How to Prepare for the Test

Drinking a lot of water and other fluids the night before the test may help to get the sample.

How the Test Will Feel

You will need to cough. Sometimes the health care provider will tap on your chest to loosen deep sputum. There may be a steam-like mist to inhale to help you cough up the sample.

Why the Test is Performed

The culture is done on the sputum to help identify the bacteria, or other type of germs, that are causing an infection in the lungs or airways (bronchi). The doctor may collect a sputum sample the office or in the hospital.

The culture can prevent the need for more invasive procedures such as bronchoscopy.

Normal Results

In a normal sputum sample there will be no disease-causing organisms present. Often, bacteria that normally live in the mouth will grow in a sputum culture. This does not mean that you have a lung or airway infection.

What Abnormal Results Mean

If the sputum sample is abnormal, the results are called "positive." Identifying the bacteria, fungus, or virus may help diagnose the cause of:

• Bronchitis
• Lung abscess
• Pneumonia
• Tuberculosis
• Flare up of chronic obstructive pulmonary disease or cystic fibrosis

Risks

There are no risks with this method of obtaining a sample, although severe coughing might cause some chest discomfort.

Considerations

Sometimes a Gram stain or acid fast bacilli (AFB) stain of the sputum done at the same time can help make the diagnosis.

Alternative Names

Sputum culture

References

Limper AH. Overview of pneumonia.In: Goldman L, Schafer AI, eds.Cecil Medicine. 24th ed.Philadelphia,PA: Saunders Elsevier; 2011:chap 97.

Torres A, Menendez R, Wunderink R. Pyogenic bacterial pneumonia and lung abscess. In: Mason RJ, Broaddus VC, Martin TR, et al, eds.Murray and Nadel’s Textbook of Respiratory Medicine. 5th ed.Philadelphia,Pa: Saunders Elsevier; 2010:chap 32.

Updated: 4/12/2012

Reviewed by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Denis Hadjiliadis, MD, Assistant Professor of Medicine, Division of Pulmonary, Allergy and Critical Care, University of Pennsylvania, Philadelphia, PA. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.