Factor VIII assay
Factor VIII Assay
A factor VIII assay is a laboratory test used to determine the concentrations of factor VIII, a protein necessary for normal blood clotting, in a person's blood. It is the most reliable way to detect hemophilia A, a disorder that reduces a person's ability to make clotting factors. Knowing the levels of factor VIII present in a person's system is important for diagnosing and treating clotting disorders such as hemophilia A.
Preparation for the Test
Before the factor VIII assay is performed on a sample, the sample is usually centrifuged to separate any red cells from the plasma. Red cells will interfere with the assay, thus they are removed beforehand to ensure accuracy of the test. Then, buffer is added to the plasma to keep it from clotting and taking it out of solution.
Procedure of the Test
The Factor VIII assay is a chromogenic immunoassay, thus it involves the reaction of an enzyme-labelled antibody with substrate to produce a coloured product. In this particular assay, the antibody used binds to factor VIII, and when an enzyme-labelled antibody is added to the reaction, it triggers a reaction with the substrate that forms a coloured product, which can be measured for an accurate reading. Additionally, a calibrator is also included in the assay to measure the amount of factor VIII present in the sample relative to the calibrator.
Types of Assay
- Reptilase time assay: this is a clotting time test, wherein human plasma with reptilase (snake venom) is used for conversion of fibrinogen to fibrin and then the clotting time is monitored.
- Chromogenic substrates assays: this test uses chromogenic substrates to determine the levels of factor VIII by measuring the amount of product formed after the enzyme modifies the substrate.
- Immunoassays: this assay involves the use of antibodies that are specifically made to target factor VIII and measure it in a sample.
Risks of the Test
The main risk associated with Factor VIII assays is the risk of contamination of the sample with other clotting factors, such as factor IX, which can lead to false-positive results. Other risks associated with the test include false-negative results due to the inability of the antibodies to bind to the target molecule and interference from other proteins in the sample. For these reasons, it is important to ensure that all sample preparation and assaying are done in a controlled environment.
Why is the Test Performed?
The factor VIII assay is usually performed to help diagnose and monitor the treatment of hemophilia A and other hereditary bleeding disorders. It is also used in follow-up and monitoring of individuals with unknown bleeding episodes. Additionally, the test is sometimes used to monitor the effects of anticoagulant therapy, such as warfarin.
When to Perform the Test
The factor VIII assay is typically performed when a person is experiencing signs and symptoms of a bleeding disorder, such as excessive bleeding from minor wounds or bruises, heavy menstrual bleeding, and spontaneous nosebleeds. The test may also be ordered when a person has a family history of hemophilia or is undergoing treatment with anticoagulants. Additionally, it is sometimes recommended for newborn babies, especially if their mother has a history of blood clotting problems.
