FVIII inhibitors appear in about 25% of severe hemophilia A patients. They are most common in patients with inversions, large deletions and nonsense mutations. Inhibitor titer varies 1000-fold; high titer seriously impairs treatment efficacy. Inhibitors can be transient or persistent. and appear irrespective of which FVIII concentrate is selected. High titer patients are treated with high doses of human or porcine concentrate. View the FVIII product pages for kits and assays for FVIII Inhibitor measurements.