Adenosine deaminase (ADA) is a protein that is produced by cells throughout the body and is associated with the activation of lymphocytes, a type of white blood cell that plays a role in the immune response to infections. Conditions that trigger the immune system, such as an infection by Mycobacterium tuberculosis, the bacteria that causes tuberculosis (TB), may cause increased amounts of ADA to be produced in the areas where the bacteria are present. This test measures the amount of adenosine deaminase present in pleural fluid in order to help diagnose a tuberculosis infection of the pleurae. Pleurae are membranes that cover the chest cavity and the outside of each lung. Small amounts of pleural fluid are continuously produced to lubricate the movement of the lungs against these membranes and the membranes against each other during inhalation and exhalation. A variety of conditions and diseases, including infection, can cause inflammation of the pleurae (pleurisy or pleuritis) and can lead to excessive pleural fluid accumulation (pleural effusion). Tuberculosis can spread into the lungs and pleurae, causing symptoms such as chest pain, chronic cough, and shortness of breath. Since these symptoms may also be seen with a variety of other conditions, it is important to determine the cause as rapidly as possible in order to properly treat the affected person. Detecting mycobacteria in pleural fluid can be difficult because there may be a large volume of fluid and very low numbers of bacteria present. Though the ADA test is not specific and does not replace the culture for diagnosing TB, it may be positive even when numbers of bacteria are very low and can be used as an adjunct test to help determine whether tuberculosis is the likely source of a person’s symptoms.
How is the sample collected for testing?
A sample of pleural fluid is collected by a healthcare practitioner with a syringe and needle using a procedure called thoracentesis. Rarely, other body fluid samples, such as peritoneal or cerebrospinal fluid (CSF), are collected using procedures specific to the fluid type.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.