Hematocrit & blood donations

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  • #14424
    Adam Fern

    Hello all,

    I’ve been working with UA (Sam Naney) since the beginning of this year in preparation for a trail marathon I’m running in a few weeks. I donated blood (technically platelets and plasma) last weekend and it got me thinking about hematocrit.

    The apheresis machines used for the blood donation can differentiate between RBC, platelets, and plasma. Depending on the donation being performed, the phlebotomist configures the machine to take some combination/quantity of each blood component. Whichever blood parts are not donated get “rinsed back” into the patient with a saline solution. (If you’re any kind of engineer or medical nerd, they’re really cool machines!) During my last donation the tech came over to the machine, went into a setting menu, and changed my hematocrit from 42% to 43%, which I had never seen them adjust before. At the beginning of each donation a small blood sample is taken for testing and then the donation is adjusted accordingly. The tech informed me that my hematocrit had increased by a point since my last donation and she was putting this info into the machine.

    Now to the point: from some very basic web research I understand that long-duration aerobic training generally decreases hematocrit as it increases blood plasma volume. (Hematocrit is the percentage of total blood volume which is RBCs. Lower hematocrit = larger percentage of blood volume is plasma.) My first question for the group is: why does this happen? What purpose does increasing plasma volume have for the body’s adaptation to this kind of aerobic stress?

    The second half of my question has to do with training methods designed to increase hematocrit. A close friend of mine has a childhood friend who is a pro cyclist on the Trek-Segafredo team. From my friends stories, I’ve heard that training in the heat and/or lengthy sauna sessions serve to increase hematocrit (RBC volume), or at least that’s what his pro cyclist friend does. The other method that seems obvious to me is hypobaric/hypoxic training. The biggest adaptation during an acclimatization is an increase in RBC production.

    Does anyone here track their hematocrit? Do you care? Do you do anything to increase or decrease it intentionally? Is a lower or higher hematocrit level beneficial for endurance sports?

    Sorrynotsorry for the lengthy post and thanks in advance for any responses!


  • Inactive
    Anonymous on #14461

    I’ll do my best to explain this based on my layperson’s understanding. Hypervolemia is the process of expanding blood volume. Endurance training causes hypervolemia. In the early stages (2-4 weeks) the response is mainly increased plasma volume. After that increased RBC are usually observed in response to chronic endurance training. The evolutionary advantages that these afford are increased heat tolerance and increased cardiac filling and ejection volume. Both of of which have a positive effect on endurance performance.

    Increased hematocrit allows more oxygen to be carried to the working muscles so directly affects endurance performance. This is why blood doping in sports is banned. The earliest method of this was to re-infuse your own previously withdrawn blood and was called blood packing. In the mid ’80s synthetic erythropoietin (a hormone that stimulates red blood cell production) was invented to help leukemia patients whose bone marrow was not producing enough red blood cells. In the sports world this allowed a more sophisticated way to boost RBC (illegally). Since synthetic erythropoietin is indistinguishable from the real McCoy it was undetectable. Overnight, erythropoietin became endurance sport’s magic bullet.

    Sport governing bodies test hematocrit and do not allow athletes to compete when it is above about 50 (depends on sport). Crit levels above 50 pose a significant risk of stroke.

    Crit levels can be increased by training at altitude and even sleeping in a hypoxic environment (altitude tent or room). Dehydration raises crit levels. Both these factors can push crit into the danger zone for high altitude mountaineers. When I returned from K2 I had a crit of 54.

    There is a genetic mutation, polycythemia vera that causes the bone marrow to produce excessive red blood cells, boosting crit well into the 50s. Athletes with his disorder are granted special dispensation from WADA but have to take active measures to keep their crit to below the legal limit, I have trained one Olympian with this disorder and it is like being naturally blood doped.

    But I have also trained some very successful World Classe athletes and alpinists with crits in the low 40s who still can climb 8000m peaks in record times and stand on Olympic podiums.

    I suggest focusing on the training Sam gives you and that your hematocrit do its thing naturally.


    Adam Fern on #14480


    Thank you for the thorough reply! I’m certainly not looking to “train my hematocrit,” rather was curious about the natural, physiological factors which cause the body to increase/decrease hematocrit and its implications on aerobic performance.

    I’d say you addressed those things quite well.

    Thanks again,

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