Alan Adler was an expert on porphyrins, the types of colored compounds seen in blood, chlorophyll, and many other natural products. He and Dr. John Heller, MD, studied the blood flecks on the STURP sampling tapes [Heller and Adler, Applied Optics 19, (16) 1980]. They converted the heme into its parent porphyrin, and they interpreted the spectra taken of blood spots by Gilbert and Gilbert. They concluded that the blood flecks are real blood. In addition to that, the x-ray-fluorescence spectra taken by STURP showed excess iron in blood areas, as expected for blood. Microchemical tests for proteins were positive in blood areas but not in any other parts of the Shroud.
Several claims have been made that the blood has been found to be type AB, and claims have been made about DNA testing. We sent blood flecks to the laboratory devoted to the study of ancient blood at the State University of New York. None of these claims could be confirmed. The blood appears to be so old that the DNA is badly fragmented. Dr. Andrew Merriwether at SUNY has said that "… anyone can walk in off the street and amplify DNA from anything. The hard part is not to amplify what you don’t want and only amplify what you want (endogenous DNA vs contamination)." It is doubtful that good DNA analyses can be obtained from the Shroud.
It is almost certain that the blood spots are blood, but no definitive statements can be made about its nature or provenience, i.e., whether it is male and from the Near East.