Recent reports regarding inconsistencies in the blood testing results of Tyler Hamilton have continued to fuel the speculation that all successful cyclists are doped.   Two of <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" /?>
Hamilton?s blood samples from August 19 ^th to September 18 ^th showed ?mixed-blood cells? according to the Union Cycliste International (UCI), thus raising the suspicion about doping.   To date, erythropoietin (EPO) has been the most commonly used performance enhancer in cycling. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /?>

EPO is a hormone naturally produced by the kidneys when oxygen supply is low.   Thus natural EPO concentrations in the blood increase when a cyclist is anemic, has been training at altitude, or has been exposed to pollution or second-hand cigarette smoke.   EPO acts as a signal for the bone marrow to increase the rate at which red blood cells are made and released into the circulation (this can be measured as the reticulocyte count).   The increase in number of red blood cells leads to an increased oxygen supply to the tissues throughout the body.   This oxygen rich blood then acts as a signal to the kidneys to stop producing EPO keeping the hematocrit within the normal range.   It is documented that the endurance process is improved in athletes with an increased red blood cell level, and thus an increased oxygen carrying capacity.   This occurs whether the red blood cells are increased via transfusion, or artificially with r-EPO.   Improvements in performance are greatest about three weeks after r-EPO injection.

EPO is rapidly cleared from the blood stream, meaning that EPO use three or four days before a urine screen may go undetected.   Athletes and trainers have learned to manipulate EPO regimens to dodge drug tests.   In response, alternative detection methods have been focused on abnormally high hematocrit levels.   In
Geneva in 1997, the UCI implemented an upper level of normal for hematocrit of 50%, and 2.4 for the reticulocyte count.   Those cyclists testing higher than these levels are then subjected to the more accurate French urine test, which is an indirect test that looks for specific biomechanical properties of synthetic EPO using sophisticated laboratory techniques (gel electrophoresis).

A new development in doping has been the increased prevalence of auto-transfusion (drawing blood from yourself, and replacing it at a later time in an attempt to boost your oxygen carrying capacity). Fear of being caught for EPO use, and awareness of the difficulty of testing for auto-transfusion, has driven athletes to self-transfusion. In preparation for the Sydney Olympics, Australian officials did research quantifying mixed red blood cell populations via the flow cytometric technique used to detect minute differences between fetal and maternal blood cells in pregnant women.   This method is accurate in detecting the small amount of mixed blood cells that would result from an auto-transfusion.   Using more specific antigen testing, authorities can more specifically hone in on blood types, exposing those who may have been doped.   The half-life of transfused red blood cells is 55 days, meaning that this test could possibly detect doping from up