It transpires that, of the approximate 21,000 genes in the body, several hundred turn on when an athlete has taken EPO or undergone a blood transfusion. They have also discovered that this change in the athlete’s genetic signature will remain detectable for weeks – maybe months – after the doping took place.
The level of precision means genetic sequencing could provide an important supplement to the two forms of biological-passports currently used to detect for blood-doping. The urine test for EPO only works within 48 hours after doping took place, so it is unlikely to catch athletes who cheated outside of competition to increase their training capacity.
The blood-passport system, meanwhile, is designed to expose only significant variations in the composition of red-blood cells. As a result, cheats can avoid detection fairly easily either by microdosing or through diluting their blood, most commonly with a saline infusion or by drinking lots of water.