Colin Berry, in a posting entitled, “Blood-grouping the Shroud of Turin – like trying to sort apples from oranges in the dark wearing boxing gloves," writes:
You can do it one two ways, masterfully described recently by Kelly P. Kearse (a self-styled “card-holding immunologist) with a gift for exposition on the Other Site. . . .
[ . . . ]
My own position at present (which could change in the light of new evidence) can be simply expressed. Any real blood on the Shroud of Turin that still responds to tests for “blood”, e.g. porphyrins, albumins, physiological electrolytes (Na, K, Ca, Mg,P etc) is unlikely to be medieval blood, far less 1st century. That’s not to say that real blood was not deposited on the Shroud at the time of its genesis by whatever mechanism, or whether that blood preceded the body image or not. Anything that tests as intact non-degraded albumin, or still immunologically-competent “blood group AB”, assuming those tests are not ‘false positives’ (which they may well be) is probably of relatively recent addition.
The only thing that would convince me that blood stains, if real, support authenticity is radiocarbon dating.
Given there is still alleged blood on the Shroud that can, we are told, be detached as scrapings without damaging the linen, then why not test- date some blood immediately? Why were blood flakes not included in the original C-dating protocol anyway?