A toxicology report after his death found high levels of carboxyhemoglobin, an indicator of carbon monoxide in the blood, according to a statement from Randall Zúñiga, the director of the Costa Rica Judicial Investigation Agency. Miller Gardner’s test showed a saturation of 64 percent, he said, adding that anything over 50 percent was lethal.

Miller Gardner, the teenage son of former New York Yankees outfielder Brett Gardner, died of carbon monoxide poisoning, authorities in Costa Rica said Wednesday night.

When carboxyhemoglobin saturation exceeds 50%, it is considered lethal. In Gardner’s case, the test showed a saturation of 64%.