The institute's CEO Khalid Galant said on Thursday Adoro, who placed seventh in the race in June, was notified of the sample tested positive for prednisone and a high level of testosterone.
He will now face a charge of doping at an independent tribunal.
In June, winner of the 2012 Comrades Marathon Ludwick Mamabolo tested positive for methylhexaneamine – a stimulant commonly found in some training supplements.
"Testosterone is also naturally produced by the body and when a sample tests positive for testosterone beyond a threshold value [level] it indicates an abnormal level in the body and requires further investigation. A carbon isotope ratio mass spectrometry (Cirms) analysis is performed to determine whether the high concentration is naturally produced by the body, or artificially introduced through other means," explained Galant.
He added: "As per the protocol for testosterone cases, we have to rule out endogenous production of testosterone and any medical abnormality before releasing the athlete's name. The investigation has revealed the result was due to an anti-doping rule violation, and a charge will be filed against the athlete."
Galant said Adoro's case would be passed on to the Lesotho sports authorities to rule on the matter.