What is qualitative chemical analysis?
Qualitative chemical analyses, designed to detect the presence of specific substances, confirm blood. If they detect one, it is almost certainly present. Such tests are designed to have no or few false positive results. The tests can be repeated with fresh reagents by independent observers, and the results should agree. There are usually multiple tests for the same compounds or functional groups. Detection limits are generally known. If a material is not detected, it can probably safely be rejected. Analytical results can be used objectively to test many different hypotheses.
The page ties back to the blood identification on the Shroud.