Paul-Bunnell test

Alternative names
Heterophil agglutination test; Forssman antibody test

The Heterophil agglutination test is a means of detecting two antibodies in the blood that indicate infection with the Epstein-Barr virus (EBV).

How the test is performed

Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

For an infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

The sample is then taken to the laboratory and the serum separated from the cells. Part of the serum is mixed with sheep red blood cells and part with horse red blood cells.

How to prepare for the test
No special preparation is necessary.

For infants and children:
The preparation you can provide for this test depends on your child’s age and previous experience. For specific information regarding how you can prepare your child, see the following topics:

  • Infant test or procedure preparation (birth to 1 year)  
  • Toddler test or procedure preparation (1 to 3 years)  
  • pPreschooler test or procedure preparation (3 to 6 years)  
  • Schoolage test or procedure preparation (6 to 12 years)  
  • Adolescent test or procedure preparation (12 to 18 years)

How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed
Your health care provider may use this test to aid in the diagnosis of infectious mononucleosis and illness caused by (EBV).

Normal Values
The Paul-Bunnell and Forssman antibodies react with sheep and horse red blood cells causing clumping. No clumping (agglutination), with a titer lower than 1:56, is the normal result.

What abnormal results mean
If the titer rises to around 1:220 in the 3rd or 4th week of infection, then gradually decreases in the following 4 weeks, infectious mononucleosis may be diagnosed.

What the risks are
Risks associated with having blood drawn are slight:

  • Excessive bleeding  
  • Fainting or feeling lightheaded  
  • Hematoma (blood accumulating under the skin)  
  • Infection (a minimal risk any time the skin is broken)  
  • Multiple punctures to locate veins

Special considerations
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Johns Hopkins patient information

Last revised: December 6, 2012
by Dave R. Roger, M.D.

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