Monday, February 1, 2016

From the Athlete's Heart Mailbag: Blood Donation

by Larry Creswell, M.D.

We invited readers to submit heart-health questions for Dr. Larry Creswell. Periodically through the coming months, Larry will devote his column to answering questions that should be of interest to triathletes and other endurance athletes. If you have a question, contact Larry by e-mail.


From Adam: What’s the deal with giving blood and endurance sports?

I gather from Adam’s longer email that he regularly donates blood. We should thank Adam for his generosity.

Adam is also an endurance athlete and wants answers to a set of related questions:

What are the short-, medium-, and long-term consequences of blood donation on athletic performance?

When are the best times to give/not give?

Let’s start with a primer on the blood itself, talk about blood donation in general, and then finish up with some thoughts about blood donation specifically for endurance athletes.

The Blood
The typical adult has about 5 liters of blood. We call this amount the blood volume and it depends a bit on both gender (women have less) and body size (smaller individuals have less).

The blood is made up of two components: the liquid, known as plasma, and a variety of blood cells suspended in that liquid.

The plasma makes up about 55% of the blood volume. This fluid is mostly water, but it contains a variety of important proteins and dissolved substances such as glucose and electrolytes. One important set of plasma proteins are those that help the blood to clot, the so-called clotting factors.

The cells account for the remainder of the blood volume. The majority of cells are the red blood cells that transport oxygen to the body’s tissues. There is a smaller number of white blood cells. A third important cell is the platelet which is involved in blood clotting.

Each individual has a blood type: A, B, AB, or O. This designation refers to the presence of antigens found on the surface of the individual’s red blood cells. The blood type is used to select compatible blood for individual patients who require transfusion.

Blood Donation
In medical practice, there is a constant need for donated blood to treat patients with a variety of medical problems. At this point, unfortunately, there is no suitable artificial blood substitute. According to estimates from the American Red Cross, more than 5 million Americans need blood transfusions each year. In this country we depend upon nearly 50,000 volunteer blood donors each day to supply this needed blood.

There are four types of blood donation:

  1. Whole blood - This is what we typically think of when we say that somebody donated a “pint of blood” (about 450 mL, or 7% of the blood volume) and is the most common form of donation. After donation, the whole blood is separated into its transfusable components: the red blood cells, the plasma, the platelets, and cryoprecipitate (a subfraction of the clotting proteins). In this sense, a single blood donor can provide components that will be transfused into four different patients. Donors are allowed to donate whole blood every 56 days. The plasma fluid is replenished by the body within 24 to 48 hours, but replacement of the red blood cells takes about four to eight weeks.

  2. Red blood cells alone - For this type of donation, a special apheresis machine is used that collects the red blood cells and returns the remainder of the blood to the donor. Donors typically donate 2 units of red blood cells, so this form of donation is called double red cells. Donors are allowed to donate red blood cells every 112 days.

  3. Plasma - An apheresis machine is used to collect only the plasma portion of the blood; the cells are returned to the donor. Donors are allowed to donate plasma every 28 days. There is a special need for plasma donors with the rare AB blood group because this plasma is compatible with all recipients.

  4. Platelets - An apheresis machine is used to collect platelets and return the remainder of the blood to the donor. This type of donation can be particularly valuable because the amount of platelets obtained from a single donor can be as large as the amount gathered from 12-18 whole blood donors. Donors are eligible to donate 24 times per year. There is a special need for platelet donation from donors with the rarer A+, B+, and AB+ blood groups.

Blood Donation and the Endurance Athlete
Platelet donation would have only a modest effect on the typical endurance athlete. The other forms of donation, though, have important physiologic effects because of relative dehydration (due to loss of blood volume) or loss of the blood’s oxygen-carrying capacity due to the removal of red blood cells.

The absolute impact of donation for an individual athlete will depend upon several factors: body size, gender, the particular sport or activity, the general health of the athlete, and the nutritional status of the athlete, and others.

One recent report (Hill, Vingren & Burdette) illustrates the consequences of blood donation by endurance athletes particularly well. Investigators studied 19 young male and female cyclists who donated either approximately 700 mL of plasma or approximately 450 mL of whole blood. Their performance on exhaustive cycle ergometer tests were measured before and then 2 hours, 2 days, and 7 days after donation. For athletes who donated whole blood, there was a significant reduction in VO2max -- 15% after 2 hours, 10% after 2 days, and 7% after 7 days. In contrast, there was no significant change in VO2 max after plasma donation. Instead, there was a decrease in measures of anaerobic capacity such as maximal accumulated oxygen deficit -- 15% at 2 hours, 9% at 2 days, and 4% at 7 days.

Some Practical Considerations for the Endurance Athlete

  • Recreational athletes can typically donate blood throughout the year. Elite and competitive amateur athletes should carefully weigh the options and timing for blood donation.
  • Discuss blood donation with your physician and your coach.
  • Because of blood donation’s effects on athletic performance, consider donating whole blood during the off season or at another time that allows for a several-week period of recovery before important training or competition.
  • Donation of platelets or plasma will have the least and shortest-lived impact on athletic performance.
  • Even mild iron-deficiency can prolong the time needed to regenerate donated red blood cells.
  • Remember that any sort of chronic medical condition may delay recovery from donation.
  • Stay well-hydrated immediately before and after donation.
  • Use caution about the intensity and duration of training immediately after donation.

References
Hill DW, Vingren JL, Burdette SD. Effect of plasma donation and blood donation on aerobic and anaerobic responses in exhaustive, severe-intensity exercise. Appl Physiol Nutr Metab 38:551-557, 2013.


Larry Creswell, M.D., is a cardiac surgeon and Associate Professor of Surgery at the University of Mississippi Medical Center in Jackson, Mississippi. In addition to his regular column on Endurance Corner, he maintains The Athlete's Heart blog to offer information about athletes and heart disease in an informal way and to encourage exchange and discussion that will help athletes build a heart-healthier lifestyle. You can contact him at lcreswell@umc.edu.
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