The suspended RadioShack-Nissan rider Frank Schleck says his 'B' sample has also come back positive for a banned diuretic, though he continues to deny any wrongdoing.
The former Tour de France podium finisher from Luxembourg quit the Tour in disgrace Wednesday after being informed by the International Cycling Union of a positive test for Xipamide.
Schleck, who finished third on the race last year, could have continued in the race under UCI rules but the 32-year-old's embattled RadioShack team sent him home.
Diuretics are not considered performance-enhancing but can be used to help riders lose weight, and therefore perform better in the tough mountain stages of the race.
More ominously, they can also conceal the presence of a banned drug by helping to flush it from the body through increased urination. Xipamide, a diuretic, is normally used for the treatment of oedema and hypertension.