Ruth Chepngetich, the women's marathon world record-holder, has been provisionally suspended for a positive doping test on Thursday.
Chepngetich tested positive for a banned diuretic and masking agent, hydrochlorothiazide or HCTZ, in March and "opted for a voluntary provisional suspension while the AIU's investigation was ongoing," the Athletics Integrity Unit (AIU) said.
The Kenyan runner set the world record by almost two minutes at the Chicago Marathon last October in 2 hours, 9 minutes, 56 seconds. It was her third win in Chicago.
The AIU said HCTZ is used clinically to treat fluid retention and hypertension, adding that diuretics may be abused to mask the presence in urine of other prohibited substances.
The 30-year-old also won the marathon at , where the women's race started at midnight to avoid extreme daytime heat.
In April, Chepngetich withdrew from the London Marathon, saying at the time she was "not in the right place mentally or physically" to race her best.
The AIU gave no timetable for a disciplinary case.
