The test of the 35-year-old journeyman took place out of competition in March 2012 and after being recently reanalyzed using new scientific methods was found to contain the banned blood booster.
The UCI has a policy of stocking and retesting results going back ten years.
"The strategy, implemented by the Cycling Anti-Doping Foundation (CADF), provides that samples from the leaders of the Grand Tours, UCI World Championships and general rankings of all cycling disciplines will be stored for potential retesting," the UCI said in a statement.
"Other samples, based on risk assessment carried out by the CADF, laboratory recommendations, Athlete Biological Passport data, new detection methods and scientific developments, will also be retained for retesting. The standard time of storage and further reanalysis under this strategy is up to 10 years."
The Katusha team for which Caruso has competed since 2012, said they would await the result of the 'B' sample before taking any measures.
The Russian team had selected the Sicilian for the upcoming Tour of Spain which gets underway this weekend.
Caruso, who started his professional career in 2002 with the Spanish ONCE team, finished fourth in the one day classic Liege-Bastogne-Liege race last April.
The Italian's best result in a major Tour was 12th in the 2006 Giro d'Italia.