Erythropoietin (EPO) is a naturally occurring hormone primarily produced by the kidneys that plays a central role in the body’s red blood cell production. This hormone signals the bone marrow to create more red blood cells, which are responsible for carrying oxygen throughout the body. Hematocrit, on the other hand, is a measurement that indicates the percentage of red blood cells in a person’s total blood volume. Athletes may seek to manipulate these levels to gain a performance advantage by increasing oxygen delivery to their muscles.
EPO’s Role and Impact on the Body
When the body experiences low oxygen levels, specialized cells in the kidneys increase erythropoietin (EPO) production. This stimulates the bone marrow to accelerate red blood cell formation.
An elevated red blood cell count enhances oxygen transport throughout the bloodstream. This increased oxygen delivery benefits muscles, allowing them to perform more efficiently during strenuous activity. For endurance athletes, this improves stamina and overall performance, which explains why artificial EPO manipulation is prohibited.
What is a Hematocrit Test?
A hematocrit test quantifies the proportion of red blood cells within a blood sample. This measurement provides insight into the blood’s oxygen-carrying capacity.
The test involves drawing a blood sample, which is then sent to a laboratory. There, the sample is spun in a centrifuge, separating blood into its components. Red blood cells settle at the bottom, allowing their volume to be measured relative to the total blood volume. Normal hematocrit ranges for adult men are 38.3% to 50%, and for adult women, 34.9% to 44.5%.
Using Hematocrit to Detect EPO Abuse
Administering synthetic EPO externally leads to an overstimulation of red blood cell production, resulting in unnaturally high hematocrit levels. Anti-doping agencies have historically monitored these levels as an indirect indicator of potential doping.
Some sports federations once used specific threshold values, such as a hematocrit of 50% for males and 47% for females, as triggers for further investigation. Exceeding these thresholds does not automatically result in a doping violation but signals a need for more in-depth examination.
This approach aims to identify athletes whose blood profiles deviate significantly from physiological norms, suggesting potential enhancement of oxygen transport. The elevation in red blood cell volume can thicken the blood, which carries health risks for athletes.
Why Hematocrit Testing Alone is Not Enough
Relying solely on hematocrit levels for doping detection presents limitations due to various factors that can naturally influence these measurements. Dehydration, for example, can concentrate the blood and lead to an artificially elevated hematocrit reading. Similarly, individuals living or training at high altitudes often exhibit higher hematocrit levels as their bodies adapt to lower oxygen availability by producing more red blood cells. Certain medical conditions can also impact hematocrit, making it challenging to attribute an elevated level solely to doping.
Because of these confounding variables, anti-doping strategies have evolved beyond simple hematocrit thresholds. Modern approaches include direct EPO assays, such as isoelectric focusing, which can specifically identify the presence of synthetic EPO in urine or blood samples.
Additionally, the Athlete Biological Passport (ABP) is a sophisticated tool that tracks an athlete’s individual blood parameters, including hematocrit, hemoglobin, and reticulocytes, over time. The ABP establishes a unique baseline for each athlete, and significant deviations from this personal profile, rather than a single high reading, can indicate potential doping and prompt further targeted testing.