For plasma donation your red cells are put back IMMEDIATELY so your body hasn't had the opportunity to make more. Thus the ratio of red cells to plasma does not change. In doping, red cells are removed and stored in refrigeration. While in storage, your body replaces them both with red cells stored in the spleen, and newly manufactured ones, bringing your percentage of red cells (about 40-45% of blood volume, called the hematocrit) back to normal. Once back to normal, the stored red cells are added before the athletic event, giving you a HIGHER than normal hematocrit. Nothing is detectable. Officials could measure your hematocrit and see it is higher than normal, but they could not prove this didn't occur naturally.