Anti-P antibody

	Tweet

Alternative names
Donath-Landsteiner test

Definition
This is a test that detects the Donath-Landsteiner antibody in serum (the portion of blood without cells), which may be related to paroxysmal cold hemoglobinuria.

How the test is performed

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

In infants or young children:
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.

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

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

• infant test or procedure preparation (birth to 1 year)
  
• toddler test or procedure preparation (1 to 3 years)
  
• preschooler 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
This test is sometimes performed when the diagnosis of paroxysmal cold hemoglobinuria is suspected.

Normal Values
No presence of antibodies is normal.

What abnormal results mean

Abnormal results indicate Paroxysmal cold hemoglobinuria (PCH), a disorder that results from the presence of an antibody to the so-called “P-antigen complex” on red blood cells. This antibody is also referred to as a Donath-Landsteiner antibody. Reduced temperatures somehow cause the antibody to bind to the P-antigen on red blood cells. This causes destruction of red blood cells (complement-mediated hemolysis); and hemoglobin (a protein in red blood cells) is excreted in the urine. (See complement.)

PCH is an acquired syndrome. The appearance of the antibody has been associated with viral infections (for example, measles and mumps) and with syphilis. However, in rare cases there is no apparent disease-related association.

What the risks are

• excessive bleeding
  
• fainting or feeling light-headed
  
• Hematoma (blood accumulating under the skin)
  
• infection (a slight 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.

Medical Encyclopedia
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | 0-9