Should You Drink Water Before Having Blood Drawn?
Updated: Apr 17
When preparing for a blood draw, whether for blood work or blood donation, it is always a good idea to drink plenty of water beforehand. Blood plasma, which comprises about 55% of blood, is over 90% water! Every time you have blood drawn, nearly half of it is water leaving your body. Consequently, your level of hydration can have a direct impact on your blood draw experience.
According to the U.S. National Academies of Science, Engineering, and Medicine, an adequate daily fluid intake is about 15.5 cups a day for men and 11.5 for women. Several factors, such as exercise and environment, influence what constitutes an adequate amount. While each person has a different adequate amount of fluids they need to consume on a daily basis, it is recommended you drink an additional three glasses of water in the three hours leading up to your blood draw.
The Benefits of Drinking Water Before A Blood Draw
You have likely heard stories about people experiencing dizziness or fainting while giving blood. One of the primary reasons it is recommended to hydrate before a blood draw is to reduce the side effects that can occur with blood loss.
Lowering the volume of your blood can result in your heart rate or blood pressure dropping temporarily, which may cause dizziness. Drinking a bottle of water right before your draw will increase your blood volume and can reduce your chances of feeling lightheaded.
Not every blood draw will have side effects, and unless you’re having large quantities of blood drawn, it’s unlikely you’ll have any side effects at all. However, drinking water beforehand is still recommended, as there are additional benefits that will help your draw go quickly and smoothly.
Your draw will go more quickly. When you drink water, your blood becomes thinner, and it can travel more easily through your veins.
It will be easier for the phlebotomist to locate your vein to start the draw. As your blood volume increases, your veins become plumper and more visible.
After Your Blood Draw
Drinking water does not end when your blood draw begins. After your draw, your body will need water to begin replenishing the blood that was lost, making it important to continue consuming fluids. It’s also advisable to not consume alcohol or caffeine afterwards, which can both cause dehydration and delay recovery.
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