https://www.sciencedirect.com/science/article/abs/pii/S2468170917300218
Just see this article. The question of accuracy in older samples need to be addressed. Moreover sensitive tests mihgt pick up older stains, but specificity would be lacking due to false positives. Last but not the least the amount of blood available also matters. There are so many variables.
Statement from the above article:
Actual bloodstain age correctly predicted with 70% accuracy for up to two years
Further articles
https://pubmed.ncbi.nlm.nih.gov/19576708/
Article Immunochromatographic Detection of Human Blood: A Forensic Review
That's what we're looking for. Currently, they are trying to analyze human samples that are about 200 years old.
Melissa Kindt
It's just the beginning. and a few methodologies.
Most presumptive detection systems are based on the peroxidase-like activity of the heme component. If the stain has been dry and not otherwise environmentally assaulted, positive presumptive tests will most likely be positive over many decades/centuries (?). However, confirmational tests for human speciation relies on immunological tests for blood serum proteins and/or DNA-RNA. In comparison, these blood components, while quite stable, can be degraded by environmental effects. So, it depends!
As of current, the oldest blood sample that has ever been detected and identified as being of a homo sapien origin is 5,300 years old. We know that it is human, but the quality of the sample is quite poor because of freezing temperatures and the passage of time. I am unsure whether or not you are seeking this information from a modern forensic standpoint or an anthropological standpoint, but I hope this article helps. https://www.nationalgeographic.com/history/article/120502-oldest-blood-otzi-iceman-mummy-oetzi-zink-science
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