The World Anti-Doping Agency (Wada) has launched an investigation after it emerged that the sample of a British Cycling rider contained traces of the steroid nandrolone after a test in late 2010.
Wada has told BBC Sport that it has now asked its Intelligence and Investigations Department to look into the matter, and to seek further information from UK Anti-Doping (Ukad).
Nandrolone is known as a 'threshold substance', where the amount found in a sample needs to be above certain thresholds to trigger action by an anti-doping organisation.
Back in late 2010, Ukad is understood to have told British Cycling that one of their riders' samples had contained a low level of nandrolone, possibly on the basis that it could be because of a health issue or a contaminated supplement.
Wada's investigation is likely to examine whether either of these explanations were established as the cause, and what further action may have been taken by Ukad.
The inquiry will focus on why British Cycling then conducted its own private testing of riders after the positive test. Wada's code appears to compel Ukad - not a governing body such as British Cycling - to undertake such an investigation.
When contacted, Ukad said it could not confirm or comment on individual test results, but in a statement a spokesperson said: "We are working with Wada to investigate claims relating to private testing carried out by British Cycling in 2011.
"Ukad is examining archives to confirm decisions that were taken in 2011 followed due process set by Wada.
"Sometimes amounts of a 'threshold substance' can be reported by the laboratory in a negative sample which are found to be below the threshold where an investigation is required.
"These are trace amounts and can sometimes occur in the body naturally.
"The guidance from Wada is that these trace findings may be used to help to decide who gets tested and when in the future, but does not automatically lead to an investigation.
"We work within the Wada framework and are always happy to work with them if they ever require any further information from us on any of our activities."
A British Cycling spokesman said: "We are unable to give full comment on this story at this stage as the events took place over 10 years ago and none of the senior management team involved have worked for British Cycling for some time.
"We are reviewing such archived records that exist from this period and, although that is not a straightforward or quick process, we will share the findings with the relevant parties."