“The IAAF can confirm that an anti-doping rule violation case concerning Jemima Sumgong (Kenya) has commenced this week, the International Association of Athletics Federations said in a statement.
"The athlete tested positive for EPO (Erythropoietin) following a no-notice test conducted by the IAAF in Kenya.
"This was part of an enhanced IAAF out-of-competition testing program dedicated to elite marathon runners which is supported by the Abbott World Marathon Majors group."
If Sumgong's B sample is confirmed as positive and she is subsequently banned it will be a massive blow for African distance powerhouse Kenya, where her Rio victory was greeted with near-delirium after such a long and inexplicable barren spell over the classic distance at the Olympics.
Kenya took silver in the women's marathon at the three previous Games and a bronze in 2000 having failed to medal before that after the race was introduced to the Games in 1984.
Sumgong, 32, had a stellar 2016, winning the London Marathon in April then claiming the elusive Olympic gold in Rio despite being disturbed by a protester on the course.
Sumgong's former compatriot Eunice Jepkirui, who switched allegiance to Bahrain in 2013, took silver.
Eliud Kipchoge won the men's race to complete a Kenyan double.
The latest cases will be seen by observers as evidence of how the IAAF is making progress in the region after previous official criticism of anti-doping regimes in Kenya and Ethiopia.
Both countries have in the past been deemed non-compliant with the World Anti-Doping Agency's (WADA) code.
-The Star