Epo profiles obtained by double-blotting. Panel A is reproduced from Beullens et al.^1(Fig1A), and panels B and C are results from our laboratory. (A) Lane 1 shows epoetin β; lane 2, darbepoetin α; lane 3, urine sample considered as “false positive” (the arrow shows a white hole corresponding to ineffective transfer of proteins in this area); and lane 4, the same sample as in lane 3 1 hour later. (B) Lane 5 shows a mixture of epoetin β and darbepoetin α; lane 6, natural urinary Epo from a sample taken after strenuous exercise (note some shift toward the cathode of the banding pattern); lane 7, natural urinary Epo; lane 8, urine sample showing the protein (P) unrelated to Epo outside the window of integration (dotted box) used for interpretation of an antidoping control result; and lane 9, urine sample in case of epoetin administration (note the difference with the natural urinary Epo pattern even in the case of the post-strenuous exercise sample). (C) Two-dimensional electrophoresis of a urine sample showing both Epo and protein P.