Adenosine Deaminase Test

The adenosine deaminase test is used to measure the amount of the adenosine deaminase (ADA) enzyme in a sample of blood. It is also known as the ADA test. The test is commonly used as part of the evaluation of tuberculosis (TB), a bacterial infection that mostly affects the lungs.

The ADA enzyme plays an important role in the development and function of lymphocytes (white blood cells), especially T lymphocytes. It also helps change monocytes (a type of white blood cell) into macrophages (a special type of white blood cell). In people with TB, ADA levels increase because T cells are activated. Deficiency of ADA manifests as a severe decrease in lymphocytes and immunodeficiency. Thus, ADA has been proposed to be a useful surrogate marker of TB.

You may be advised to get the adenosine deaminase test if you are experiencing symptoms or signs of an underlying infection, inflammation, or other medical conditions. The test is usually ordered along with other investigations. If TB is suspected, the symptoms may include:

• Chills (shivering due to feeling cold)
• Rise of temperature in the evening
• Loss of appetite
• Weakness
• Fatigue
• Chest pain
• Cough that goes on for more than 3 weeks

The following categories of people are advised to get the test:

• Individuals being evaluated for TB – This test may be recommended as part of a diagnostic evaluation for people with symptoms of TB.
• Individuals with signs of infection or inflammation – This test may be used in combination with other tests to identify the underlying cause.

The ADA test may be used with other tests to help diagnose certain conditions, such as:

• Tuberculosis – This is a bacterial disease that affects various parts of the body, most commonly the lungs followed by the kidney, spine, and brain.
• Adenosine deaminase (ADA) deficiency – This is a rare immune system disorder that impairs the development and function of lymphocytes, making the body more vulnerable to infections.
• Deficiency of adenosine deaminase 2 (DADA2) – This is a rare condition that causes inflammation of the blood vessels and other tissues in the body.
• Infectious mononucleosis – This is a condition caused by viruses, most commonly the Epstein-Barr virus.
• Typhoid– This is an infection caused by Salmonella typhi, a type of bacteria. It is characterised by fever, rash, and diarrhoea.
• Sarcoidosis – This is an inflammatory disease in which the immune system forms tiny clusters of inflammatory cells called granulomas in different organs. These granulomas can interfere with normal organ function if they persist.
• Leukaemia – This refers to the cancer of blood cells.
• Brucellosis – This is a condition caused by contact with animals infected with the Brucella bacteria.
• Rheumatoid arthritis – This is an autoimmune condition characterised by pain and swelling in the joints.

What to Expect Before the Adenosine Deaminase Test

No fasting is required for a standalone Adenosine Deaminase test. You can eat and drink normally. However, if it is part of a broader package that includes fasting tests, your doctor may advise fasting for 8-12 hours. Avoid strenuous exercise for 24 hours before the test, as intense physical activity can temporarily raise Adenosine Deaminase levels and affect interpretation. Always inform your doctor about any ongoing medications.

What to Expect During the Blood Collection

A phlebotomist cleans the skin with an antiseptic, then places an elastic band around your upper arm to make the veins easier to access. A small needle is inserted into the vein; you may feel a brief pinch. Blood is collected into a labelled tube in under a minute.

What to Expect After the Adenosine Deaminase Test

A small cotton swab and bandage are placed over the site to stop any minor bleeding. You can return to normal activities immediately. Minor bruising is normal and disappears quickly. If dizzy, sit and rest for a few minutes.

In the ADA test, the primary parameter being measured is:

• The level of adenosine deaminase in a sample of blood.

The ADA test normal range is indicated in the table below.

Note: Normal values may differ slightly between laboratories. A doctor should always interpret the results along with the symptoms and clinical findings.

The ADA test interpretation is given in the table below.

The ADA test is a simple blood test. However, it has some risks and limitations that should be known:

Risks:

• The test is usually safe and involves minimal risk. You may feel slight pain when the needle is inserted or mild bruising afterwards, which usually resolves spontaneously.

Limitations:

• The ADA test cannot diagnose any conditions on its own; further tests are needed to confirm a diagnosis.
• An abnormal ADA level is not specific to a single disease. Increased or decreased levels can occur in different conditions.

Depending on your symptoms, medical history, and results, your doctor might recommend the following tests to help identify the underlying cause:

• Sputum acid-fast bacillus (AFB) test
• TB blood test-interferon-gamma release assay
• TB skin test (Mantoux tuberculin skin test)
• CD4 lymphocyte count
• HIV antibody test
• HIV antibody/antigen test
• NAAT (Nucleic acid amplification test) test