No blood residue had previously been detected, however, despite various studies detailing his violent death due to an arrow shot and other injuries.
"There were no [blood] traces found, even when they opened some arteries, so it was thought maybe the blood had not preserved and had completely degraded, or that he lost too much blood because of the arrow injury" on his back, said team member Albert Zink, head of the Institute for Mummies and the Iceman in Bolzano, Italy.
For the new investigation, scientists traced Ötzi's wound areas—the arrow injury and a cut on his right hand—with a pioneering nano-size probe.
Each minute movement of the probe was recorded with a laser, "so you get a three-dimensional image of the sample in a very tiny scale," Zink explained.
The scans revealed classic "doughnut shape" red blood cells, the team reported Wednesday in the journal Interface.
(Related: "Iceman Bled Out From Arrow Wound, X-Ray Scan Reveals.")
While past studies have suggested evidence for prehistoric blood on Stone Age tools and other artifacts, "you can never really be sure, because you can see structures which are quite similar to red blood cells" such as pollen grains or bacteria, Zink commented.
To confirm they were indeed dealing with human blood cells, the researchers illuminated the wounds with a laser. The wavelengths of the scattered light revealed the substances' molecular makeup.
"We got very typical samples for blood, like for the [blood protein] hemoglobin," he said.
The new finding "really is the oldest clear evidence for red blood cells."
(Related: "Wounded Iceman Made Epic Final Journey, Moss Shows.")
Quick Death
The new nanotechnology, allied with an atomic force microscope, also uncovered traces of fibrin, a blood-clotting agent—evidence that the Iceman suffered a mercifully quick demise.
