Factor V assay

Answer 1

Definition

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

How the test is performed

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The area is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. 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, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

How to prepare for the test

No special preparation is needed.

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

This test is used to find the cause of too much bleeding (decreased blood clotting).

Normal Values

The value is normally 50 - 200% of the laboratory control or reference value.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What abnormal results mean

Decreased factor V activity may be related to:

• Deficiency of factor V that is present at birth (congenital)
• Disseminated intravascular coagulation (DIC)
• Liver disease(such as cirrhosis)
• Primary fibrinolysis

What the risks are

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.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

This test is most often performed on people who have bleeding problems. The risk of excessive bleeding is slightly greater than for people without bleeding problems.

Special considerations

When you bleed, the body launches a series of activities that help the blood clot. This is called the coagulation cascade. The process involves special proteins called coagulation factors (factor V is a coagulation factor).

Each factor's reaction triggers the next reaction. The final product of the coagulation cascade is the blood clot. Blood clots may not form normally if any one of the clotting factors is abnormally low.

References

Kessler C. Hemorrhagic disorders: Coagulation factor deficiencies. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 180.

Answer 2

Definition

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

How the test is performed

A blood sample is needed. For information on how this is done, see: Venipuncture

How to prepare for the test

No special preparation is needed.

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

This test is used to find the cause of too much bleeding (decreased blood clotting).

Normal Values

The value is normally 50 - 200% of the laboratory control or reference value.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

What abnormal results mean

Decreased factor V activity may be related to:

• Deficiency of factor V that is present at birth (congenital)
• Disseminated intravascular coagulation (DIC)
• Liver disease(such as cirrhosis)
• Primary fibrinolysis

What the risks are

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.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

This test is most often performed on people who have bleeding problems. The risk of excessive bleeding is slightly greater than for people without bleeding problems.

Special considerations

When you bleed, the body launches a series of activities that help the blood clot. This is called the coagulation cascade. The process involves special proteins called coagulation factors (factor V is a coagulation factor).

Each factor's reaction triggers the next reaction. The final product of the coagulation cascade is the blood clot. Blood clots may not form normally if any one of the clotting factors is abnormally low.

References

Gailani D, Neff AT. Rare coagulation factor deficiencies. In: Hoffman R, Benz EJ Jr., Shattil SJ, et al, eds. Hoffman Hematology: Basic Principles and Practice. 5th ed. Philadelphia, Pa: Churchill Livingstone Elsevier; 2008:chap 127.

Kessler C. Hemorrhagic disorders: Coagulation factor deficiencies. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 180.

Reviewed By

Review Date: 02/28/2011

David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.