What is the Paul-Bunnell test (Mononucleosis test)?

From the Guidelines

The Paul-Bunnell test is a diagnostic blood test used to detect heterophile antibodies in patients suspected of having infectious mononucleosis (mono), but it has largely been replaced by more specific and sensitive tests like the monospot test and EBV-specific antibody tests. The Paul-Bunnell test works by identifying antibodies that agglutinate sheep or horse red blood cells, which appear in about 80-90% of patients with mono caused by Epstein-Barr virus (EBV) 1. The test is performed by mixing the patient's serum with sheep red blood cells and observing for agglutination. A positive result strongly suggests infectious mononucleosis, though false negatives can occur, particularly in children under 10 years old and in the early stages of infection. Some of the key points to consider when interpreting the results of the Paul-Bunnell test include:

• The test is not as sensitive or specific as newer tests, such as the monospot test or EBV-specific antibody tests 1
• False negatives can occur, particularly in certain patient populations, such as children under 10 years old 1
• The test is rarely used in modern clinical practice, having been largely replaced by more accurate and reliable tests 1 It is worth noting that the Paul-Bunnell test remains historically significant as one of the first serological tests for infectious mononucleosis, but its use is no longer recommended in modern clinical practice due to the availability of more accurate and reliable tests. Some of the alternative tests that can be used to diagnose infectious mononucleosis include:
• Monospot test: a modified heterophile antibody test that is more sensitive and specific than the Paul-Bunnell test 1
• EBV-specific antibody tests: these tests can directly detect viral antigens or antibodies and provide more accurate results than the Paul-Bunnell test 1

From the Research

Definition and Purpose of the Paul-Bunnell Test

• The Paul-Bunnell test, also known as the Mononucleosis test, is used to diagnose infectious mononucleosis, a disease caused by the Epstein-Barr virus (EBV) 2, 3, 4.
• The test detects the presence of heterophile antibodies in the blood, which are a type of antibody that reacts with sheep red blood cells 5, 6.

How the Test Works

• The Paul-Bunnell test involves mixing a patient's serum with sheep red blood cells to see if the antibodies in the serum will agglutinate (clump) the red blood cells 3, 5.
• If the test is positive, it indicates the presence of heterophile antibodies, which are a hallmark of infectious mononucleosis 2, 4.

Limitations and Alternatives

• The Paul-Bunnell test is not always reliable, especially in young children, and may produce false-negative results 3.
• Other tests, such as the Monospot test and ELISA, may be used to confirm the diagnosis of infectious mononucleosis 2, 5, 6.
• The Monospot test is a simpler and more rapid test that can be used to detect heterophile antibodies, but it may not be as sensitive as the Paul-Bunnell test 5.

Clinical Significance

• The Paul-Bunnell test is still an important tool in the diagnosis of infectious mononucleosis, despite the development of more modern immunologic methods 4.
• The test can help clinicians diagnose infectious mononucleosis and distinguish it from other diseases that may present with similar symptoms 2, 3.