Test for precipitating antibodies

Alternative names
Aspergillus immunodiffusion test; Aspergillosis precipitin

Definition
This is a laboratory test to detect antibodies in the blood resulting from exposure to the fungus Aspergillus.

How the test is performed

Blood is drawn from a vein 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.

Using immunologic testing techniques, the blood sample is examined for precipitin bands that form when aspergillus antibodies are present.

How to prepare for the test
There is no special preparation.

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

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
The test is performed when a fungal infection is suspected.

Normal Values

The normal test result is negative for aspergillus antibodies.

What abnormal results mean

Precipitins are found in 95% of cases involving a fungus ball. About half of hypersensitivity pneumonitis (allergic bronchopulmonary Aspergillosis, also called ABPA) cases have precipitins. Invasive aspergillosis often gives a false-negative precipitin test (Aspergillus is present, but the test is negative.)

What the risks are

The risks are associated with having blood drawn:

     
  • Excessive bleeding  
  • Fainting or feeling light-headed  
  • Hematoma (blood accumulating under the skin)  
  • Infection (a slight risk anytime 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 Simon D. Mitin, M.D.

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.