UCI and hematocrit
So, does it mean that when a rider is deemed "unfit" for competition he has tested positive for a performance enhancing substance? No, of course not. Since the use of EPO and blood-doping can be tricky to detect directly through doping tests, the UCI decided to prevent possible cheaters from riding, by establishing a hematocrit limit.
But why measure hematocrit? And why has the limit been set at 50%? Both the choice of measuring hematocrit and the limit of 50% is, in my opinion, a poor testing procedure. I say this, not because I'm advocating the use of PEDs, but because 50% hematocrit damages honest, clean riders. After prolonged training at altitude, many athletes will naturally test above the 50% limit, without any PEDs in their system. The test itself is also a bit weak, since dehydration and activity before testing could affect the result. If you have been standing up for more than 30 minutes and then sit down to take the test, you could have much higher values, due to the increased heart rate and blood-pressure.
Why not measure, and establish limits for hemoglobin values instead? This would be more accurate and prevent some of the problems we are experiencing today. 50% hematocrit value for a male athlete is too low (it corresponds to about 16.5 g/dl of hemoglobin). If the UCI wanted to continue to measure hematocrit, at least increase the value to 55% (around 18.5 g/dl of hemoglobin).