In diagnosing hemophilia, a physician will perform a complete physical examination and compile a thorough medical history. A family history of hemophilia can be a strong indicator that a patient may have this disorder.

Coagulation tests also may be ordered to measure levels of clotting factor and to monitor how long it takes blood to clot. From these results, a physician can tell not only whether or not a patient has hemophilia, but also the type of hemophilia (type A or B) that is present and its level of severity. Hemophilia is diagnosed in one of the following three severities:

Severe hemophilia is more likely to be diagnosed very early in a child’s life. It is often recognized during the child's first year because it tends to cause severe bleeding in babies. Children with other forms of hemophilia may not be diagnosed until they are older.

Pregnant women can have their fetus tested for the presence of hemophilia. This is usually done through chorionic villus sampling (CVS) or amniocentesis. CVS is usually performed nine to 10 weeks into the pregnancy and involves the analysis of a sample of chorionic villi taken from the placenta. Amniocentesis is usually done 16 weeks into the pregnancy and involves an analysis of fetal cells taken from a sample of the amniotic fluid in the uterus. Because very little can be done based on the results of these tests, they are rarely recommended.

If a patient has experienced serious internal bleeding from hemophilia, imaging tests such as ultrasounds or MRIs may be used to view the joints and any damage that may have occurred.