By doing a blood test for certain antigens.
Someone who has hydrocephalus cannot give blood. I do not know why. It is just stipulated by the transfusion guidelines (google it).
One can find out what blood type they have by going and getting their blood tested at a hospital or the doctors. If you give blood they will i've you a card and tell you what your blood type is on the card.
Only doctors know that.
Go to rhe doctors and get a blood test
Yes. If you take a drug test, doctors will know by the elements in your blood, as drugs stay in your body for some time, and that may be a long time in cases.
so they can draw the blood type and save someones life
The doctors only know and for how it seems..... I'm not one.
It is important to know your ''blood type'' (as it is referred to) because if you need blood, your body will only accept the blood that is your ''blood type'' Another reason, is that if you ever have the need to ''give'' blood, you can only ''give'' blood to someone who has your ''blood type''. It is advisable to carry around a card with blood type, in case of an emergency and you need blood. It will save time having the labs take your blood and test it while you might be dying.
Fairly obviously I think, doctors don't know exactly when someone is going to die, and to give such a prediction serves no useful purpose, and opens one up to ...
people say it is rare to get a diseases by using other peoples mascara but I don't know for sure.
Carlisle buys the blood, as he is a doctor with a high status. If you read those few chapters it mentions how doctors can purchase blood. I don't know if doctors really can buy blood or not but that's what Stephenie Meyer uses in her story.
Ideally, someone with a blood type O should receive a blood transfusion from someone who also has the same blood type. One can have their blood type tested by donating blood.