Kenya's former London Marathon winner Daniel Wanjiru has been banned for four years for doping.
The Athletics Integrity Unit said it was "highly likely" that Wanjiru used prohibited substances, citing abnormalities in his biological passport.
The 28-year-old, who had been provisionally suspended in April, won the London Marathon in 2017 and the Amsterdam Marathon in 2016. He will be banned until December 8, 2023.
A blood test from March 9, 2019, showed an "extraordinarily high" haemoglobin level, the AIU said.
"We therefore confirm our previous opinion that it is highly unlikely that this profile is the result of a normal physiological or pathological condition, and it is highly likely that it was caused by the use of prohibited methods, with or without the use of prohibited substances," the AIU reported.
In April, Wanjiru proclaimed his innocence, arguing that the biological passport "is confusing and frustrating."
His Netherlands-based management agency, Volare Sports, issued a statement on Thursday, backing Wanjiru's innocence.
"We are very disappointed about this decision," the company said. "We emphasise that no prohibited substance has ever been found and we strongly believe that Daniel is innocent."
Wanjiru, who has until early November to appeal, has not returned a positive test, but an athlete's blood passport can reveal the effects of doping by interpreting sample results taken over an extended period.