During blood donation 8-10% of the blood volume is removed. Most people adapt quickly to this loss and experience no ill-effects, but a few individuals adapt less well and consequently feel faint.
Feeling faint can happen to anyone. However, some people are more likely to feel faint than others:
- People who weigh less than 50kg are more likely to feel faint if they give blood because they lose relatively more of their blood volume than larger people. This is why women and young donors are more likely to faint than men and donors over 20 years of age.
- People donating blood for the first time are more likely to feel faint than people who have donated many times previously. Because of this, we recommend that you read Preparing for your blood donation before you come in for your first donation.
- People who miss meals and who don’t drink enough fluids before and after donating will recover more slowly from blood donation.
- Standing still for long periods of time can lead to pooling of blood in the legs. This reduces the amount of blood available to the brain and can make you feel light-headed or faint.
- Being in a hot room or sitting or standing in the sun causes the blood vessels to dilate (that is why you look flushed in the heat). This causes less blood to be available to circulate to the brain which can lead to dizziness and fainting.
- Rushing about, or vigorous exercise, can also produce similar effects.
- If you drink alcohol within a few hours of giving blood you are more likely to feel faint. This is because alcohol also dilates the blood vessels.
- Fainting or feeling faint can happen during the blood donation, and may also occur for up to 6 hours after you leave the blood donor centre.
- If you faint after leaving the donor centre you may fall or injure yourself. If you are driving and you feel faint, it is important to pull over as soon as possible and lay your car seat flat. Do not attempt to keep driving.
What can I do to prevent fainting?
The likelihood of fainting can be minimised if you follow the following advice:
- You should drink 3 good-sized glasses of water/juice before your donation. At least 2 of these glasses should be drunk on your arrival at the Donor Centre. Be prepared by having plenty of liquid in the 24 hours before donation, especially in warm weather.
- Make sure that you eat something in the 3 hours before donating – savoury and salty foods are best.
- If you usually have low blood pressure and feel faint when you stand up suddenly or you have previously fainted, please tell us before your donation. Our staff can assist you.
- Tense and relax your calf and thigh muscles repeatedly and move your legs and feet during your donation.
- Spend at least 15-20 minutes in the refreshment area and have a cool drink and salty snack after donating to allow your blood volume to adjust.
To reduce your chance of fainting after you have left the Blood Donor Centre, for the next 6 hours:
- Continue to drink plenty of cool ﬂuids but avoid alcoholic and hot drinks.
- Avoid standing still for long periods, do not rush or do strenuous exercise or have a hot shower.
What to do if you feel faint
If you feel faint or unwell whilst you are at the Blood Donor Centre please tell a staff member immediately.
If you feel faint after you have left the donor couch, immediately sit or lie down as ﬂat as possible to avoid falling and injuring yourself and:
- Remain lying down for around 30 minutes or until you feel well again.
- Whilst lying down, tense your calf and thigh muscles for 5 seconds, then relax, and repeat this 5 times and continue to do this every 1-2 minutes until you feel better.
- Sit up for at least 4-5 minutes before you stand up.
- Drink plenty of cool ﬂuids (at least 2 good sized glasses) and have a savoury snack before you leave.
- Do not drive for at least 6 hours after you have recovered because there is a small risk that you may faint again whilst you are driving If you feel faint whilst you are driving, slow down and stop the car as soon as it is safe to do so. Remain in the car, and lay your seat as ﬂat as possible. It is recommended that you do not get out of your car as fainting beside a road can be hazardous. Do not attempt to drive again. Call 000 for an ambulance.
Please let us know
If you have any of these symptoms or other concerns whilst at the Blood Donor Centre please let staff know immediately so they can assist. If you develop any symptoms after you leave the Blood Donor Centre, and you require urgent attention, first seek attention from a hospital or doctor so the problem can be assessed. If you do see a doctor we would like to hear the outcome – please call us and ask to speak to a medical officer on 13 14 95.
If you are unsure whether you should seek medical attention, or you are worried about anything following your donation please call us for advice on 13 14 95 and ask to speak to one of our medical officers.