What's the difference between somebody with hemophilia a and someone with hemophilia b?

Different factors. The difference is in the clotting factor missing. Hemophilia a is caused by lack of the blood clotting factor viii. Hemophilia b is caused by a lack of blood clotting factor ix. They both lead to the inability of blood to clot properly, just in different ways.
Deficiency factor 8. The difference is that hemophilia a is due to a deficiency of factor 8 (viii), while hemophilia b is from a deficiency of factor 9 (ix). Both are sex-linked recessive, and both have similar lab findings of a normal pt and high ptt. The treatment of each is replacement of the respective factors. Hemopnilia a gets factor 8 while hemophilia b get factor 9 in concentrates or fresh frozen plasma.

Related Questions

What is the difference between hemophilia a and hemophilia b?  

Hemophilias. Hemophilia is a bleeding disorder, usually inherited with an x-linked recessive inheritance pattern, which results from the deficiency of a coagulation factor. Hemophilia a results from the deficiency of clotting factor viii. Hemophilia b results from the deficiency of clotting factor ix. Acquired hemophilia is a separate noninherited condition, rarer than congenital hemophilia, autoimmune.
Bleeding disorder. Hemophilia a is due to the absence of clotting factor viii (most common) hemophilia b is due to the absence of clotting factor ix (less common).