Adenosine Deaminase

The adenosine deaminase (ADA) test is not a diagnostic test, but it may be used along with other tests such as pleural fluid analysis, acid-fast bacillus (AFB) smear and culture, and/or tuberculosis molecular testing to help determine whether a person has a Mycobacterium tuberculosis infection (tuberculosis or TB) of the lining of the lungs (pleurae).

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).

An ADA test may be ordered when a person has an accumulation of fluid in the chest cavity (pleural fluid) and has signs or symptoms that suggest TB, such as:

• Chronic cough, sometimes with bloody sputum
• Fever, chills
• Night sweats
• Unexplained weight loss
• Chest pain

This test may be ordered as one of several tests to help rule in or rule out TB as the cause of a person’s symptoms, especially if the individual falls into a high-risk group, such as:

• People with close contact with someone who has active infectious TB
• Immigrants from areas of the world where the incidence of TB is high
• Children younger than 5 years old who have a positive TB screening test
• 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
• People with weakened immune systems such as:
  • Those with HIV/AIDS
  • Those with chronic underlying conditions, including diabetes and kidney disease
  • Organ transplant recipients and others on immunosuppressant drugs
  • Pregnant women
  • The elderly

Testing may be ordered when a healthcare practitioner wants to determine whether a person likely has tuberculosis, in advance of other test results, in order to initiate treatment.

If adenosine deaminase (ADA) is markedly elevated in pleural fluid in a person with signs and 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 lupus. 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.

The ADA test cannot positively identify M. tuberculosis as the cause of a person’s symptoms, and the test results cannot be used to determine if the person has drug-resistant tuberculosis.

A healthcare practitioner cannot diagnose tuberculosis in the pleural space without testing the pleural fluid. If the infection is present in your lungs, then sputum may be collected or, if meningitis is suspected, cerebrospinal fluid (CSF) would be tested.

The ADA test is primarily performed when tuberculosis is suspected in the pleurae, and it is not routinely available in all laboratories. It will be performed when a healthcare practitioner determines that it will be useful and timely in helping to diagnose or rule out tuberculosis.

Yes, and it sometimes is, but it is done for another purpose and not to detect tuberculosis. The blood may be tested to help identify ADA deficiency.

ADA is an enzyme that converts one byproduct into another byproduct. The first substance is toxic to lymphocytes and must be inactivated by ADA. With ADA deficiency, a rare inherited condition, the body makes insufficient ADA. This leads to the buildup of the toxic byproduct and can cause severe combined immunodeficiency disease (SCID). Infants with this condition have seriously compromised immune systems and may not survive without bone marrow transplantation. For more information, visit the Genetics Home Reference webpage on ADA deficiency.