Factor XII assay

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Factor XII assay

Definition:

Factor XII assay is a blood test to measure the activity of factor XII -- one of the substances involved in coagulation (blood clotting).

Alternative Names:
Hageman factor assay
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. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood.

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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. A bandage may be applied to the puncture site if there is any bleeding.

How to prepare for the test:

There is no special preparation needed for adults.

For infants and children:

The preparation you can provide for this procedure depends on your child's age, previous experience, and level of trust. 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)
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, you may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed:

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.