When factor levels fall below 5%, you’re at the highest risk for bleeds and joint damage, and that risk continues to increase the lower your factor levels get. When factor levels drop from 5% to 1%, it cuts bleed protection by nearly a third.

When your factor levels are above 10%, you are at a much lower risk for bleeds. Trough levels above 15% mean you can be confident you’re protected from bleeds — it's predicted that people with factor levels this high will typically average just one bleed every two years.

When discussing factor levels, it’s important to differentiate peak factor levels and trough factor levels.

Peak factor levels occur right after an infusion. This is when your factor levels will be highest and you’re most protected from a spontaneous bleed. After this, they will start to decline, returning to their lowest point before your next infusion. This low point is called your trough level.

This is when you are most vulnerable to a bleed. Your routine treatment should be keeping your trough factor levels high enough to protect you from bleeds, even at the lowest point before your next infusion. Trough levels are important for you and your doctor to review when evaluating your level of control.