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Alternative names
Hageman factor assayDefinition Return to top
This is a blood test to measure the activity of factor XII -- one of the substances involved in coagulation (blood clotting).How the test is performed Return to top
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 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.
How to prepare for the test Return to top
There is no special preparation needed for adults.How the test will feel Return to top
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 Return to top
To determine the cause of abnormal results on a blood-clotting test (PTT).
Coagulation (blood clotting) results from a sequence of reactions involving proteins known collectively as the coagulation factors. The liver produces coagulation factors and secretes them into the blood.
Normal Values Return to top
A normal value is 50-200% of the laboratory "control" or reference value.What abnormal results mean Return to top
Decreased factor XII activity may indicate:What the risks are Return to top
Special considerations Return to top
Factor XII deficiency is not normally associated with clinical bleeding and Factor XII does not appear to be necessary for the formation of clots for normal hemostasis (stopping of bleeding).
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Page last updated: 28 October 2004 |