A culture is considered the "gold standard" for diagnosing tuberculosis and guiding treatment, but it may take several days to weeks to complete. Molecular testing and the AFB smear are rapid tests, but they require that a sufficient number of microorganisms be present in the fluid to detect them. Pleural fluid presents a unique problem with detecting M. tuberculosis because there may be a large volume of fluid with a very low number of bacteria present. Though the ADA test is not definitive, it is a rapid test and may be elevated even when there are few bacteria present. ADA results may be used to help guide treatment until results from a culture are available.
The ADA test is used as an adjunct test to help rule in or rule out tuberculosis in pleural fluid. Rarely, it may be ordered to detect tuberculosis in other body fluids, such as peritoneal fluid or cerebrospinal fluid (CSF).
People who work with or are part of groups with high rates of infection, such as the homeless, IV drug users or confined populations, such as hospitalized patients, prisoners, and residents of nursing homes
If adenosine deaminase (ADA) is markedly elevated in pleural fluid in a person with symptoms that suggest tuberculosis, then it is likely that the person tested has a M. tuberculosis infection in their pleurae. This is especially true when there is a high prevalence of tuberculosis in the geographic region where a person lives.
When there is a low prevalence of tuberculosis in a region, then a person may have tuberculosis or may have an ADA result that is elevated for another reason, such as cancer (particularly lymphomas), pulmonary embolus, sarcoidosis, or systemic lupus erythematosus. These other diagnoses are more likely if the ADA result is only mildly or moderately elevated.
A person with a low ADA level is unlikely to have tuberculosis in their pleurae. This does not rule out having the infection in other parts of their body.
If ADA is markedly elevated in fluid from another part of the body (such as peritoneal fluid or CSF), then there is an increased likelihood that tuberculosis is present in this area.
This article was last reviewed on May 18, 2012. | This article was last modified on October 8, 2014.
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