| Definition: |
A test that detects the Donath-Landsteiner antibody in serum (the portion of blood without cells), which may be related to paroxysmal cold hemoglobinuria.
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| Alternative Names: |
Anti-P antibody
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| How the test is performed: |
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (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 veins below the tourniquet to distend (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 tourniquet 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.
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. |
| How to prepare for the test: |
Adults:
No special preparation is needed.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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| 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. |
| Normal Values: |
| No presence of antibodies is normal. |
| What abnormal results mean: |
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); 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 acute viral infections (for example, measles and mumps) and with syphilis. However, in rare cases there is no apparent pathological (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
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| 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. |
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