Purpose of sputum and blood sample

Sputum

A sputum culture is a test to detect and identify bacteria or fungi that are infecting

the lungs or breathing passages. Sputum is a thick fluid produced in the lungs

and in the airways leading to the lungs. A sample of sputum is placed in a

container with substances that promote the growth of bacteria or fungi. If no

bacteria or fungi grow, the culture is negative. If organisms that can cause

infection grow, the culture is positive. The type of bacterium or fungus will be

identified with a microscope or by chemical tests.

If bacteria or fungi that can cause infection grow in the culture, other tests may

be done to determine which antibiotic will be most effective in treating the

infection. This is called susceptibility or sensitivity testing.

This test is done on a sample of sputum that is usually collected by coughing. Do

not use mouthwash before collecting a sputum sample because it may contain

antibacterial substances that could affect your results. For people who can't

cough deeply enough to produce a sample, they can breathe in a mist solution to

help them cough.

Blood sample

A blood culture is a test to find an infection in the blood. The blood does not

normally have any bacteria or fungi in it. A blood culture can show what bacteria

or fungi are in the blood.

A bacterial infection in the blood, called bacteremia, can be serious because the

blood can spread the bacteria to any part of the body. A blood infection most

often occurs with other serious infections, such as those affecting

the lungs, kidneys, bowel, gallbladder, or heart valves.

A blood infection may also develop when the immune system is weak. This can

occur in infants and older adults, and from disease (such as cancer or AIDS) or

from medicines (such as corticosteroids or chemotherapy) that change how well

your body can fight infections (immunity).

To test for an infection in the blood, a sample of blood is collected and placed in

a cup with special substances that allow the bacteria or fungus to grow. The type

of bacteria or fungus that grows is checked with chemical tests and by looking at

the culture under a microscope. Two or three blood samples from different veins

are often taken to make sure a bacteria or fungus is not missed. If no bacteria or

fungus grows, the blood culture is called negative. A blood culture is often done

when a person has a fever because this is the time when the bacteria or fungus

is most likely to have spread to the blood.