Blood Doping - Detection of Blood Doping

Detection of Blood Doping

A common approach to the detection of doping is the random and often-repeated search of athletes’ homes and team facilities for evidence of a banned substance or practice. Professional cyclists customarily submit to random drug testing and searches of their homes as an obligation of team membership and participation in the UCI ProTour. In 2004, British cyclist David Millar was stripped of his world time-trial championship after pharmaceutical EPO was found in his possession. Because athletes sometimes inject or infuse non-banned substances such as vitamin B or electrolytes, the possession of syringes or other medical equipment is not necessarily evidence of doping.

A more modern approach, which has been applied to blood doping with mixed success, is to test the blood or urine of an athlete for evidence of a banned substance or practice, usually EPO. This approach requires a well-documented chain of custody of the sample and a test method that can be relied upon to be accurate and reproducible. Athletes have, in many cases, claimed that the sample taken from them was misidentified, improperly stored, or inadequately tested.

Yet another detection strategy has been to regard any apparently unnatural population of red blood cells as evidence of blood doping. Red blood cell population in the blood is usually reported as hematocrit (HCT) or as the concentration of hemoglobin (Hb). HCT is the fraction of blood by volume occupied by red blood cells. A normal HCT is 41-50% in adult men and 36-44% in adult women. Hemoglobin (Hb) is the iron-containing protein that binds oxygen in red blood cells. Normal Hb levels are 14-17 g/dL of blood in men and 12-15 g/dL in women. For most healthy persons the two measurements are in close agreement.

There are two ways in which HCT and Hb measurements can suggest that the blood sample has been taken from a doping athlete. The first is simply an unusually high value for both. The Union Cycliste Internationale (UCI), for example, imposes a 15-day suspension from racing on any male athlete found to have an HCT above 50% and hemoglobin concentration above 17 grams per deciliter (g/dL). A few athletes naturally have high red blood cell concentrations (polycythemia), which they must demonstrate through a series of consistently high hematocrit and hemoglobin results over an extended period of time.

A recent, more sophisticated method of analysis, which has not yet reached the level of an official standard, is to compare the numbers of mature and immature red blood cells in an athlete's circulation. If a high number of mature red blood cells is not accompanied by a high number of immature red blood cells—called reticulocytes--it suggests that the mature red blood cells were artificially introduced by transfusion. EPO use can also lead to a similar red blood cell profile because a preponderance of mature red blood cells tends to suppress the formation of reticulocytes. A measure known as the "stimulation index" or "off-score" has been proposed based on an equation involving hemoglobin and reticulocyte concentrations. A normal score is 85-95 and scores over 133 are considered evidence of doping. (The stimulation index is defined as Hb (g/L) minus sixty times the square root of the percentage of red blood cells identified as reticulocytes.)

These threshold levels, and their specific numeric values are sources of controversy. Establishment of incorrect threshold values is one way that false positive test results can be produced by a doping control program.