What Is Sputum? - Definition, Culture & Types

Instructor: Lacey Russell

Lacey has a Master's of Science in Nursing with a specialization in Acute Care Nurse Practitioner

In this lesson we will first discover what sputum is. We will then discuss how and why sputum is cultured, go over the different types of cultures and learn how to utilize the results of the culture.

Sputum Defined

Sputum is the medical terminology word for the thick liquid that is coughed up from lungs. It can contain bacteria, tissue particles, blood, and really anything that is in the lungs. Sputum is normally clear and a little thicker than water. If it is frothy and in large amounts, this could be due to pulmonary edema (which is the buildup of fluid in the lungs).

Sputum can also be classified as mucoid or purulent. This sputum can be anywhere from white, gray, yellow, green or brown and is thicker than normal. Mucoid is usually white or gray and can be caused by chronic diseases such as COPD (chronic obstructive pulmonary disorder) and asthma. Purulent sputum is typically more yellow and green and is due to respiratory tract infections. If the sputum is blood stained it could be caused by tuberculosis, lung cancer or a pulmonary embolism, just to name a few.


A culture is a test done to determine what type, if any, of bacteria or fungus are growing in the sputum. Before the culture can be performed, the sputum must be collected. This is typically done one of three ways. The first way is to give the patient a sterile (free from bacteria) specimen cup and let them spit into the cup. This is easier said than done because a lot of patients will just spit saliva into the cup. To get a good specimen the patient must expectorate (cough up) the sputum and immediately get it into the cup while getting as little saliva as possible in the cup.

The second method only works if the patient is intubated (has a tube in their throat to breathe through). While suctioning the tube to clear the airway, a sputum trap can be attached, and the specimen collected and sent to the lab.

The third method also involves a the use of the sputum trap. While the patient is sedated, a doctor can perform a bronchoscopy. This is a procedure where a camera is inserted into the lungs to look at the lining, and any strange findings are seen on on an x-ray. While the camera is in the lungs, doctors can use suction to remove some sputum and send it to the lab.

Culture Process

The first step of the culture process is the gram stain. This is when a portion of the sputum is stained with dye and inspected under the microscope. The gram stain is just to see the shape and size of the bacteria or fungus. To decide was type it is, an actual culture must be performed.

Image of what is seen when looking at a gram stain under a microscope

To perform the culture, the sputum is spread onto a Petri dish and left in an incubator to grow for several days. Once the bacteria or fungus has grown enough to be identified, the dish is removed, and the growth is inspected with a microscope again.

Petri dish with growth

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account