All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
The blood that comes out of a wound is impure; it should be washed and the clothes that are stained with it must be purified before praying in them.
We have already stated that the blood of a human being is impure according to the view of most scholars, and that the view that it is pure is weak.
However, what is hard to avoid is forgiven, such as the blood of a wound that continues to flow, as well as little blood, according to the view of the four Imams, it is forgiven even though they differed about determining exactly what is considered to be little.
Some of them specified it by customs, such as the Shaafi'i and Hanbali Schools, and some of them determined it by the size of a Dirham, like the Maaliki and the Hanafi Schools.
Since you write to us sometimes in Arabic, then we refer you to some Fataawa in our Arabic site; so please refer to Fatwa 248944 and the Fatwa referred to in it, and Fatwa 75699 about the amount that is forgiven in impurities; as well Fatwa 150031 about what is forgiven due to hardship.
You may also refer to Fatwa 398203 on our English site.
Allah knows best.