Anti-doping officials from Sport Ireland have launched an investigation after urine samples taken from GAA players were lost by couriers on two separate occasions while en route to a World Anti-Doping Agency laboratory in Germany.
Sport Ireland has written to the GAA informing it of an investigation into the lost samples.
The Irish Independent has also learned of seven failed attempts by anti-doping officials to test GAA players between June 2016 and May 2017, involving inter-county players from Carlow, Kilkenny, Westmeath, Antrim and Offaly.
In each case, the squads were not present for testing despite their schedules being agreed months in advance.
The investigation was launched in June this year after urine samples taken from three GAA players with the Westmeath hurling team were forwarded to a WADA-approved laboratory in Cologne for testing. The samples never arrived.
This was the second time that samples had disappeared. On July 11, 2016, samples taken from three Fermanagh footballers were lost en route to Germany. In the first instance involving Fermanagh's football squad, samples were lost en route to Germany by the courier company.
Siobhán Leonard, anti-doping manager with Sport Ireland, wrote to Gearoid Devitt, player welfare administrator at GAA headquarters, telling him of the missing urine samples.
In the second instance, samples were taken from the Westmeath hurling squad on May 7, 2017. Again four samples were taken from three players, and sent to a laboratory in Germany via the courier. They were also lost. Ms Leonard again wrote to Mr Devitt in the GAA, informing him: "I am aware that this is the second time urine samples have went missing. Sport Ireland does take this matter very seriously and a full investigation has been launched with [the named courier company]."
A spokesperson for Sport Ireland told the Irish Independent that an investigation was launched by the courier company to find the missing samples, which were not recovered.
"Sport Ireland uses [the courier company] on average in excess of 1,500 times a year and as such occurrences such as this, while very serious, are extremely rare," they added.
Separately there were also two failed attempts to take samples from Westmeath GAA players earlier this year.
In April, anti-doping officials arrived to find the entire squad of hurlers absent, while in May, the Westmeath football squad was not present at a scheduled training session despite anti-doping officials being there for testing.
Westmeath GAA was handed fines of €520 and €611, respectively, for the incidents.
GAA player welfare officer Mr Devitt wrote to Sport Ireland agreeing to pay the fines and blaming a breakdown in communication.
Westmeath GAA PRO Aidan Walsh told the Irish Independent: "Last-minute changes of training venue led to miscommunication with the testers from Sport Ireland."
Anti-doping officials were also twice unable to test Carlow's Gaelic football squad in June of last year. Ronan Dempsey, operations manager with Carlow GAA, told the Irish Independent: "Last-minute changes of training venue due to inclement weather led to the miscommunication."
Only three GAA players have ever failed drug tests.