The National Forensic Science Technology Center wrote, "The line between screening and identification is not always clear. For example, while examining the clothing of a suspect, a forensic biologist might visually locate a brown stain that presumptively tested positive for blood and was then DNA typed. The DNA type is found to match the victim. Knowing that the loci tested are higher primate specific, what conclusions can be drawn?
The only unqualified conclusion that can be offered is that the stain contains DNA that matches the victim. It has not been proven to be blood.
If asked Could the results have arisen because the material tested was the blood of the victim? then an answer of Yes is justified. However, it would be wrong to report that the material was human blood with a DNA type that matched the victim. The material was not subjected to confirmatory testing for blood or proven to be human in origin."
This issue is the elephant in the room for the prosecution's conjectures about luminol. Without a true confirmatory test, the luminol-positive material cannot be said to be blood. I would also like to comment on the sensitivities of confirmatory tests for blood. The authors of one study, Hurley IP et al., Forensic Science International 190 (2009) 9197, wrote, "Positive results for human IgG were obtained with both formats. The simple direct immunodot assay was able to detect an IgG concentration of 0.1 mg/mL, while the detection limit for the sandwich immunodot assay was 0.01 mg/mL compared with the control (no IgG)...Tokiwa et al. demonstrated a detection limit of 0.022 microgram/mL using an anti-HbA0 ELISA, compared to the limit of 0.01 microgram/mL IgG detected by the present study." Hb A0 is the main form of hemoglobin in the body. Whole blood is about 55% serum and 45% red blood cells (RBCs), although there is some variation. Hemoglobin (Hb) is found in RBCs and immunoglobulin G (IgG) is found in serum. The following calculations of the sensitivities of confirmatory blood tests attempt to normalize to whole blood.
"The concentration of hemoglobin molecules in red blood cells is so high (340 mg_mL, 2.3 mM) that they almost could be said to be on the verge of crystallization." Robert C. Kerber, J. Chem. Education Vol. 84 No. 9 September 2007, 1541. Therefore, the concentration of Hb is 150 mg/mL in whole blood. 150 mg/mL divided by 2.2 x 10-5 mg/mL = 7 x 106. This is the approximate dilution factor for detection of blood by a confirmatory test for hemoglobin. Smith et al., Principles of Biochemistry, Mammalian Biochemistry, seventh edition (McGraw Hill), indicate that the average concentration of IgG is 12 mg/mL in plasma, therefore 6.6 mg/mL in whole blood. This estimate suggests that the test for IgG would detect blood up to a factor of 6.6 x 105. There are other confirmatory tests as well, such as HemaTrace. One
article from the Michigan State Police listed its sensitivity as 0.05 µg/mL, and the authors gave its maximum dilution factor of blood that would still allow for its detection as 1:16777216. Another
study provides 0.07 µg/mL as the limit of detection.
The values above might be too optimistic by a factor of ten, and yet still they would indicate that confirmatory tests for blood are quite sensitive. One possible problem is that eventually these proteins might denature (lose their biological activity--which implies a change in their three-dimensional shape or other alteration), which could keep the protein from reacting in these experiments. That is why the several-month delay in testing Rep. 199 using a confirmatory test was so unfortunate. The bottom line is that there is no reason that the FP could not have tested the luminol-positive areas with a confirmatory test.