When cooking something with eggs, I always check the eggs for bloodspots. But I wonder, if I find a blood spot, do I need to throw the whole egg away or can I take the blood out with a spoon and use the non bloody part?
See this article from Rabbi Moshe Dovid Lebovits. In short, technically you could just remove the blood spot itself. However common practice today, barring extenuating circumstances, is to throw out the entire egg.
The following poskim say the metzius is that there are no roosters at egg farms so chickens do not mate and produce eggs which are fertile. Therefore, if one does find a blood spot in an egg, all he has to do is throw out the blood spot and he then may eat the rest of the egg:
Yechaveh Da’as 3:57, Yabea Omer Y.D. 2:5, Minchas Yitzchok 4:56, Opinion of Horav Sheinberg Shlita quoted in Divrei Chachumim page 185:20. See Be’er Moshe 5:129. Refer to Aruch Ha’shulchan 66:32.
However, since eggs are inexpensive, rather than trying to remove a blood spot, some people still throw out the whole egg. (Journal of Halacha and Contemporary Society ibid:footnote 21. Refer to OU document I-184 where the opinion of Harav Hershel Schachter Shlita is quoted as saying that the women throw away any egg with a blood spot.)