Headache after blood draw. The amount of blood taken during blood donation is not at a level that will affect your health. However, after donating blood, some adverse events such as headache, drop in blood pressure, feeling of faintness, and drowsiness may be experienced. These events will subside after approximately 3–4 hours without long-term effects.
To avoid reaction after Blood Donation
See separate risk warning from a doctor for any blood donation. To help reduce the chance of serious reactions during donating, you can: Monitor your blood pressure before and after donating. Check your blood pressure after donating and follow instructions about how much you should change it.
Watch for a change in the number of hours between donating and the time when your blood test is normal. If this change is not gradual, call your doctor.
Tell your doctor if you feel light headed, dizzy or tired.
Tell your doctor if you have any signs of infection
Tell your doctor if you have any other conditions that make donating blood difficult. Your blood donation is not an adequate test for your specific health issues. See separate risk warning from a doctor for any blood donation.
For information about health concerns in pregnancy, see separate risk warning from a doctor.
What if I don’t feel well during the blood donation?
Ask your doctor if you can donate again. You may need to receive a blood transfusion, called a red blood cell transplant. Red blood cells are a type of blood cell that circulate in your body and help with organ functions. Some conditions may make donating blood difficult.
If you are on certain drugs that make you very dizzy, have a fever and a low blood pressure, or if you have a history of blood clots and have an abnormal heart rhythm, this may make donating blood more difficult or prevent you from donating. For most people, it is safe to donate blood. However, for those who have severe health problems or who have received a blood transfusion, check with your health care provider about possible treatment for them.
What are my chances of getting my blood tested?
A blood draw will probably identify the proportion of blood cells you have. A proportion of blood cells will be drawn every few hours until the amount needed is determined. These blood cells are used to determine whether your blood is safe for donation.
If you have a regular blood draw and if you are over the age of 10, your chances of a successful blood donation are about 50%.
If you have a regular blood draw and are under the age of 16, your chances of a successful blood donation are about 15%.
If you have a regular blood draw and are under the age of 18, your chances of a successful blood donation are about 5%.
If you have a regular blood draw and are at least 18, your chances of a successful blood donation are about 15%.
If you have a regular blood draw and are over the age of 25, your chances of a successful blood donation are about 4%.
If you have a regular blood draw and are under the age of 46, your chances of a successful blood donation are about 5%.
If you have a regular blood draw and are at least 26, your chances of a successful blood donation are about 6%.
If you have a regular blood draw and are at least 45, your chances of a successful blood donation are about 8%.
If you have a regular blood draw and are at least 53, your chances of a successful blood donation are about 10%.
If you have a regular blood draw and are at least 56, your chances of a successful blood donation are about 14%.
If you have a regular blood draw and are at least 57, your chances of a successful blood donation are about 8%.
If you have a blood draw and are at least 58, your chances of a successful blood donation are about 10%.
If you have a blood draw and are at least 59, your chances of a successful blood donation are about 15%.
What if I have the blood drawn at the wrong time?
Donors have the most control over when their blood is drawn. If you don’t think you will be able to donate before the time you were scheduled to have it, ask your doctor if the time is flexible enough for you. A medical appointment may be necessary if the time is too soon or the blood drawn is not enough.
