What Really Happens to Your Body After You Donate Blood: Effects, Risks and Recovery

May 24, 2023 at 1:35 am

Written by Krista Thomas, Communications Strategist, with medical direction and expertise from Dr. Suchi Pandey, Chief Medical Officer


One of the most common concerns folks have around giving blood—even those who do so regularly—is how their body reacts and responds to the blood they’ve lost. While you are certainly losing something temporarily in giving to others, a combination of carefully researched FDA recommendations that guide donation as well as many incredible physiologic processes mean you can donate with total peace of mind regarding your own safety. In this article, we dive into what guidelines exist to ensure donors don’t lose too much blood, and how your body regenerates those cells that you’ve selflessly given away.


The perfect pint

Have you ever heard the saying, “Always give 100%, unless you’re donating blood”? While blood loss is typically something we avoid, there is a certain amount of blood we can lose that has a fairly minimal, temporary effect on most individuals’ daily lives.* The average adult has 10 pints of blood in their bodies, and whole blood donations are currently capped at one pint per person—and that’s only if the donor meets a certain height and weight requirement. Other specialized products, such as plasma and platelets, may have higher pint maximums, depending on a person’s blood count, height and weight. For each blood product donated, current limitations on donation about, as well as donation frequency (56 days between most whole blood donations, 7 between platelets, 4 weeks between plasma, and 4 months between double red), are deeply rooted in this question of what happens to the body during and after donation.


What are the effects of losing blood?

As many donors can tell you, the most common side effect of blood donation is feeling more tired following donation. This is particularly true of whole blood and double red blood cell donations, as they result in temporarily lowered levels of red cells, which carry oxygen in the blood. Lower oxygen carrying capacity of the blood due to decreased red cell volume after a donation (specifically, less oxygen getting to your tissues) can make you feel tired while your body replenishes the lost red cells. In the vast majority of cases, this will improve within a few days as your body beings to rebuild its supply of red blood cells.

A temporary decrease in the amount of platelets and plasma in your body will likely not have a material impact on your daily life. Even if you were to be in a traumatic accident that involved platelet and plasma loss following your donation, FDA regulations on the amount each donor can give would prevent severe impacts related to the decreased platelet/plasma levels.


How does your body recover?

All the blood cells you donate are reproduced and replenished typically within days to weeks of the donation, depending on the type of donation (whole blood, double red, platelets, plasma). Each type of blood cell is generated by a different bodily process and therefore replenishes on a different timeline.

  • Red cells. After you donate red cells (as in double red blood cell or whole blood donations), specialized cells in your body designed to track oxygen note decreased levels in your bloodstream and catalyze the production of a protein called erythropoietin. Erythropoietin serves as a messenger, signaling to the bone marrow to generate red cells. In the days after donation, red cells are replaced at rapid rate, but it typically takes 4–8 weeks to replace all the red cells lost in a whole blood donation. Taking iron supplementation after a donation can also help ensure more rapid recovery post-donation since iron stores and hemoglobin are closely tied. We recommend whole blood donors take a low dose of iron (e.g., 18mg) for 60 days after donation to fully recover the iron lost with a single donation. (Frequent platelet/plasma donors can also benefit from taking iron supplements due cumulative red cell loss over multiple donations.)
  • Platelets. Platelets follow a similar pattern to red cells in that, when low levels are detected, a messenger is created to tell the bone marrow to ramp up production—in this case, a hormone called thrombopoietin as opposed to erythropoietin. The bone marrow produces very large cells called megakaryocytes, and these eventually break down into the platelets our body needs. After a platelet donation, platelet count typically recovers within a week.
  • Plasma. As you may know, plasma, which makes up 55% of your blood volume, is more than 90% water—so, when the phlebotomists tell you to drink water after giving blood, it really is important! In fact, chemicals in both your brain and your kidneys will be able to tell your blood volume is low on water and will accordingly initiate a number of processes to ensure you retain as much water as possible, including by decreasing how much you lose from urination. As you hydrate to replenish the water content of plasma, your body also works to recreate the many other proteins (e.g., clotting factors, antibodies) it contains, each of which has its own process for detecting low levels and creating new cells. Plasma will begin to replenish immediately and should be fully back to normal within a few days.

While the processes outlined above may seem incredibly complex, for most people’s bodies, getting blood levels back up to par is not a heavy lift in the grand scheme of the millions of processes the body undertakes on a daily basis. However, for individuals in need of a bone marrow transplant, living with severe anemia, and so many other serious long-term conditions, the difficulty of carrying out these processes is the very reason your donations are so needed and so appreciated. As a healthy donor, you can rest assured that that which you give away will be regenerated, and that which you give to others will generate new hope.


For more information about different blood products, visit our website here. For questions about blood donor eligibility, contact our Telerecruitment team at 888-723-7831 or givebloodSBC@stanford.edu.


*The small caveat here is for serious competitive athletes, which is a topic we cover in our commonly googled questions article here.


Read all PULSE 2023, issue 2 articles.