New Study Findings: Six-year study shows that all people with hemophilia at risk for developing an inhibitor

The journal Haemophilia has published the results of a six-year study called the Hemophilia Inhibitor Research Study (HIRS) that was designed to test the feasibility of conducting national monitoring for inhibitors among people with hemophilia in the United States. The study collected blood specimens on a regular basis from study participants, which were tested at CDC for the presence of an inhibitor. Data were also collected to learn who was at highest risk for developing an inhibitor. Regular testing for an inhibitor is important because the treatment to get rid of the inhibitor is more successful when an inhibitor is identified early. In the study, investigators from 17 hemophilia treatment centers located across the United States enrolled 1,163 people with hemophilia and followed them for up to 6 years to learn the best way to determine who was at risk for developing an inhibitor. HIRS investigators and CDC researchers found that people with hemophilia of all ages were at risk for developing an inhibitor and that unless people are regularly tested for an inhibitor, they can have one and not know it until it causes a severe bleeding problem. You can read the article’s abstract here.

What is Hemophilia?

Hemophilia is an inherited bleeding disorder in which the blood does not clot properly. This can lead to spontaneous bleeding as well as bleeding following injuries or surgery.
Blood contains many proteins called clotting factors that can help to stop bleeding. People with hemophilia have low levels of either factor VIII (“factor eight”) or factor IX (“factor nine”). Because of the way hemophilia is inherited, males are the most affected. The best way to treat hemophilia is to replace the missing blood clotting factor so that the blood can clot properly. This is done by infusing (giving through a needle into a vein) commercially prepared factor.

What is an Inhibitor?

Up to 1 in 5 people with hemophilia will develop an antibody (inhibitor) to the infused factor that is used to treat bleeding episodes. The inhibitor prevents the factor from working to stop bleeding. An inhibitor makes treatment for bleeding episodes much more difficult and expensive.

Main Findings from this Study

All people with hemophilia are at risk for developing inhibitors
- One-third of newly-developed inhibitors were found in people with non-severe hemophilia
- One-half were over the age 5 years
- One quarter had used infused factor for more than 150 days
- Six out of ten people with hemophilia with an inhibitor had no symptoms
Regular screening of people with hemophilia for early detection of an inhibitor by the CDC laboratory is feasible, and will inform efforts to measure rates of this complication

Critical Gaps & Future Directions

There is still much to learn about inhibitors and how to prevent and manage health problems associated with them.

Because there is no effective monitoring system, the actual number of people with hemophilia with an inhibitor in the United States is not known.
The impact of risk factors (Risk factors are characteristics, conditions, or behaviors that can increase or decrease the risk for developing an inhibitor) on inhibitors is not fully understood.
An estimated 60% of people with an inhibitor do not have symptoms, but may develop health problems from an undetected inhibitor.
People with hemophilia receiving care in federally funded hemophilia treatment centers will be tested each year for an inhibitor by the CDC Division of Blood Disorders laboratory as part of the blood monitoring program called Community Counts .

About this Study

Researchers compiled information from 1,163 people with hemophilia over a 6-year period to learn more about how to detect inhibitors and to collect information about what causes them.

CDC Activities

The Centers for Disease Control and Prevention (CDC), National Center on Birth Defects and Developmental Disabilities (NCBDDD), Division of Blood Disorders (DBD) considers inhibitors to hemophilia treatment a major public health concern and is committed to monitoring the numbers of people affected by this health problem, raising awareness about the need for inhibitor screening and promoting health education.

More Information

To learn more about hemophilia, please visit the CDC Hemophilia website.

To learn more about ongoing research in hemophilia, please visit the CDC Research page on hemophilia.

Paper Reference

Soucie JM, Miller CH, Kelly FM, Payne AB, Creary M, Bockenstedt PL, Kempton CL, Manco-Johnson MJ, Neff AT, and the Haemophilia Inhibitor Research Study Investigators. A study of prospective surveillance for inhibitors among persons with haemophilia in the United States. Haemophilia 2014; 20:230-7.