People with trough FIX levels <5% have the highest risk for bleeds. Joint bleed protection is cut by nearly a third when trough FIX levels drop from 5% to 1%.
People with trough FIX levels >5% can experience a drop in the rate of spontaneous bleeds.
People with trough FIX levels >10% have a very low risk for joint bleeds.
People with trough FIX levels >15% will average just one bleed every two years. Spontaneous bleeds are expected to be uncommon when FIX levels are >15%.