1. True. Before chemical reagents are applied to a questioned stain, it is important to examine the stained area to determine if it appears to be consistent in color & texture with blood and if there are any obvious contaminants present that could cause false-positive reactions.
2. True. Presumptive blood tests that indicate the presence of blood based on color changes caused by oxidation are done indirectly on questionable stains via rubbings onto cotton swabs or filter papers or by removing and testing very small portions of the original stain.
3. False. Presumptive tests operate based on the peroxidase-like activity of hemoglobin found within the erythrocytes (red blood cells). DNA, however, is found within nucleated cells, which in blood are the leukocytes (white blood cells).
4. True. There is a rather long and interesting history about Luminol, but most sources recognize Walter Specht of Jena, Germany as the person who introduced the concept of using Luminol as a medico-legal investigative tool in 1937.
5. False. The peroxidase activity of blood is very time stable. This writer has successfully detected the presumptive presence of blood with Luminol on archaeological artifacts shown to be approximately 8,000 years old by carbon dating.
6. True. High specificity is reflected in a presumptive blood test when the reagent does not react to many other substances other than blood or when the testing procedure allows the operator to detect false-positive reactions. Reduced phenolphthalein demonstrates the highest specificity. Still this is a PRESUMPTIVE test rather than confirmatory tests for the presence of blood.
7. False. There is no mechanism at this time that will allow a forensic biologist to determine the age of a biological stain.
8. False. Not even when multiple presumptive blood tests are used can positive findings be interpreted to mean that blood is definitely present. Other tests can be used to determine that the blood is of human origin (in general, Precipitin based tests).
9. True. Presumptive blood tests begin in the unstable, colorless reduced form and terminate in the oxidized form reflecting a color change or light emission.
10. True. An important part of good scientific protocol is to use controls when conducting experiments or laboratory analyses. A positive control (known source of blood, not necessarily of human origin) and a negative control (an unstained swab, filter paper, or area of the item being tested) ensure that the reagents are working properly in that a positive control will cause an observed reaction and a negative control will not react within the appropriate time frame. Controls must always be done first and the results documented before testing forensic evidence.
