PFC Auctions, a Guernsey-based company, announced last week that it would sell the vial of blood in an online auction set to end on Thursday.
The vial was taken at George Washington University Hospital on March 30, 1981, after Reagan was wounded by John Hinckley Jr. in Washington, DC, PFC Auctions said on its website. It is said to have come from a person whose late mother had worked at a medical lab."If indeed this story is true, it's a craven act and we will use every legal means to stop its sale or purchase," John Heubusch, executive director of the Ronald Reagan Presidential Foundation, said in a statement.
The website for PFC Auctions said the latest online bid for the vial stood at £6,270. The website for PFC Auctions showed a picture of the blood-filled vial with a label stuck to it showing the president's name.
Reagan suffered a punctured lung and internal bleeding when he was shot by Hinckley outside the Washington Hilton Hotel. Hinckley was later found not guilty by reason of insanity.
Mr Heubusch said his foundation had spoken to the hospital where Reagan was treated and was assured an investigation was under way into "how something like this could possibly happen."