Pleural Fluid for AFB Smear/ZN Stain

Specimen Required

FLUID (All Body Fluid)

Fasting Required

Purpose of the Test

The AFB smear/ZN stain of pleural fluid is performed to detect the presence of acid-fast bacilli (AFB) in the fluid. AFB are a type of bacteria that include Mycobacterium tuberculosis, the bacteria that cause tuberculosis (TB). The test is used to aid in the diagnosis of TB and other mycobacterial infections.

When this test is required

The AFB smear/ZN stain of pleural fluid is typically requested when a person has symptoms of TB, such as coughing, fever, and night sweats, and there is a suspicion of TB infection in the pleural space. The test may also be ordered in people who have been exposed to TB or who have a weakened immune system.

What the Test Detects

The AFB smear/ZN stain of pleural fluid is a microscopic examination of the fluid for the presence of AFB. The test uses a special stain, the Ziehl-Neelsen (ZN) stain, to make AFB visible under the microscope.

Preparation for the Test

No special preparation is needed for the AFB smear/ZN stain of pleural fluid. However, the procedure used to collect the fluid, thoracentesis, may require some preparation and monitoring, and it should only be performed by a qualified healthcare professional.

Sample Requirements

The AFB smear/ZN stain of pleural fluid requires a sample of fluid from the pleural space, which is collected using a procedure called thoracentesis. During thoracentesis, a needle is inserted through the chest wall and into the pleural space, and fluid is drawn out through the needle.

Additional Notes

The AFB smear/ZN stain of pleural fluid is a rapid test, but it has a lower sensitivity than a culture or molecular testing. A negative AFB smear/ZN stain of pleural fluid does not rule out TB or other mycobacterial infections, and additional testing may be needed. Additionally, the test cannot differentiate between live and dead bacteria, and it is possible to get a positive result even if the bacteria are no longer alive.

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