Kenya's Daniel Wanjiru, winner of the 2017 London Marathon, has been banned from athletics until 2023 for doping.
Wanjiru was provisionally suspended in April but denied taking a prohibited substance and requested a tribunal.
The Athletics Integrity Unit (AIU) has now confirmed the 28-year-old's ban, in place until 8 December 2023.
Wanjiru's management said they are "disappointed" by the decision and will consider an appeal through the Court of Arbitration for Sport.
"Our experts have provided a valid explanation for the anomalous blood value and have demonstrated how unlikely and unrealistic the doping scenario - as presented by World Athletics - was," the statement added.
"We emphasise that no prohibited substance has ever been found and we believe that Daniel is innocent."
Details published by the AIU state Wanjiru returned a sample showing levels of red blood cells which had no "physiological explanation".
He was tested 16 times between April 2017 and 2019. In his 14th test - on 9 March 2019 - he showed elevated levels of haemoglobin concentration.
It was concluded that the change in levels between tests could not "be explained by any other cause than blood manipulation".
The panel said it was "highly likely" a banned substance or method had been used.
Wanjiru won the 2016 Amsterdam Marathon and finished eighth and 11th at the London Marathon in 2018 and 2019 respectively.
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