Hemophilia: Exams And Tests

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Exams and Tests

Severe hemophilia is usually diagnosed in early childhood or infancy. But mild forms may not be noticed until adulthood. If a bleeding problem is suspected, the following tests from a single blood sample will help your health professional diagnose hemophilia, its type, and its severity:

• Prothrombin time (PT), which measures certain clotting factors other than those related to hemophilia. Most people with hemophilia have normal results from this test. PT results may be abnormal if another condition is causing bleeding problems.
• Activated partial thromboplastin time (aPTT) measures clotting factors VIII or IX that are absent or not working properly in people with hemophilia. If aPTT is elevated, you may have hemophilia. But this test cannot determine which type of hemophilia (A or B) is present or even if the defect is in factor VIII or IX. A person with hemophilia usually has abnormal aPTT test results.
• Factor assay test, which determines the severity of hemophilia by measuring the activity levels of factors VIII and IX in the blood, which indicate how well the factors work to clot blood.
  • Mild hemophilia: Clotting factor VIII or IX level is 5% of normal or greater. Mild hemophilia might not be recognized until excessive bleeding develops after a major trauma or surgery.
  • Moderate hemophilia: Clotting factor VIII or IX level is 1% to 5% of normal. Bleeding usually follows a fall, sprain, or strain.
  • Severe hemophilia: Clotting factor VIII or IX level is less than 1% of normal. Bleeding often happens one or more times a week for no apparent reason.
• Mixing tests, in which your plasma is mixed with normal plasma to see if it reaches a normal level of clotting factor. If the plasma doesn't reach a normal level, it may mean that your blood has developed inhibitors that are interfering with clotting factor VIII or IX. If this occurs, it may mean that you have a very rare condition called acquired hemophilia.

Genetic screening tests

If you know that hemophilia runs in your family and you are planning to have children, you can be tested for the genetic defect that causes hemophilia to determine whether you are a carrier (only females can be carriers). This will allow you to make informed decisions about pregnancy and prenatal care.

During pregnancy, health professionals can use amniocentesis and chorionic villus sampling (CVS) to test the fetus for the genetic defect that causes hemophilia. If the fetus is found to have hemophilia, you may choose whether you want to complete or terminate the pregnancy. If you decide to continue with the pregnancy, your health professional and a genetic counselor can help you learn about health issues that affect the fetus before delivery and will affect your child after he or she is born. With modern therapies and by being as careful as possible to prevent bleeding, people with hemophilia can expect to live a normal life span.²

A child can be tested for hemophilia A after birth with a sample of blood that is taken from the umbilical cord. Testing for hemophilia B in newborns is not effective because newborns naturally have lower levels of clotting factor IX. Blood tests for clotting factor IX deficiency are more effective after a child is 6 months old.

What to think about

There are many types of bleeding disorders that result from a deficiency in one or more clotting factors, although most are very rare. Von Willebrand's disease is the most common of the inherited blood disorders. Like hemophilia, von Willebrand's disease affects clotting factor VIII. But it does so in a different way than hemophilia, and it affects both males and females.

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Last updated:	August 20, 2007
Author:	Robin Parks, MS
Reviewed By:	Anne C. Poinier, MD - Internal Medicine, Brian Leber, MDCM, FRCPC - Hematology
Editors:	Kathleen M. Ariss, MS, Pat Truman