(AP) — Olympic marathon champion Jemima Sumgong tested positive for the blood booster EPO in a surprise out-of-competition doping test in Kenya, according to the IAAF.

It's the biggest blow yet to the credibility of the East African country's famed distance-running program.

Sumgong became the first Kenyan woman to win Olympic gold in the marathon at last year's Rio de Janeiro Games, is the reigning London Marathon champion, and was the points leader in the World Marathon Majors series. She was in line to receive a $250,000 bonus when the current series ends in Boston on April 17. The series said it won't name a women's winner until doping officials have resolved her case.