Athletics: Former triple Olympic champion Marion Jones said on Monday she was shocked her initial drugs test from a urine sample taken in June was positive.
Jones added she had requested the testing of her second or 'B' sample be dealt with quickly.
"I was shocked when I was informed about the positive 'A' sample," Jones said in the statement issued by her Los Angeles-area attorney Howard Jacobs.
"I have requested that the testing of my 'B' sample be expedited and done as soon as possible.
"I would also like to note that only my lawyers have the authority to speak on my behalf in this matter, and I will have no further comment until the results of the 'B' sample are released."
The comments were the first by Jones since sources said last Friday she had tested positive for the banned blood-boosting drug erythropoietin (EPO) at the US championships in Indianapolis in June.
Jones, 30, has repeatedly denied taking performance-enhancing substances and had never previously failed a doping test.
"Marion Jones has always been clear, she has never taken performance-enhancing substances, not now, not ever," Jones's general counsel Rich Nichols said in a statement to Reuters last Friday.
Jones had been under scrutiny by the US Anti-Doping Agency (USADA) in connection with the Balco Laboratory doping scandal but has never been charged with a doping offence.
Her statement did not name the substance for which her 'A' sample was positive.
If her 'B' sample is positive, she faces a two-year ban from the sport under anti-doping rules.