Chapter 10: Serology and Bloodstain Analysis Flashcards
What is serology?
Serology is the study of bodily fluids left at crime scenes.
What is the proteome?
Proteome is the set of proteins coded in the genetic makeup of an individual.
What’s the difference between a presumptive and confirmatory test?
A presumptive test is highly sensitive but not specific for a particular substance. It is general, broad, and can help rule out substances. It can give a false positive result, which is acceptable as long as no false negative results are obtained. E.g. a colour test can indicate that a stain is blood, but not what kind of blood. A confirmatory test is a test that tests positive for the substance in question and only that substance. Confirmatory tests lack sensitivity, in that a large amount of the substance must be available for the test to be positive, but a few false negatives are acceptable as long as no false positives are obtained.
Name the components of blood.
Blood is made of plasma, red blood cells (erythrocytes), white blood cells (leukocytes).
What are leukocytes and what do they do?
Leukocytes are white blood cells that are active in the immune system. Neutrophils are the most abundant white blood cell, and they work with lymphocytes which are produced in the bone marrow and thymus gland to engender the immune response. Lymphocytes produce antibodies. Macrophages support the immune response by consuming the antigens. Platelets contain no nuclei and are involved in the clotting process.
What is a blood group?
A blood group is a class of antigens produced by allelic genes at one or more loci and inherited independently of other genes. They are a robust biological marker. Blood group is a genetic trait, it is controlled by genes and unchanging throughout a person’s life.
List three presumptive tests for blood.
The tests are phenolphthalein, benzidine, leucomalachite green, and tetramethylbenzidine.
- Luminol is used for large-scale serology testing.
- Fluorescein is another chemical used to check for the presence of blood.
What’s luminol?
Luminol is a chemical that reacts in the presence of hemoglobin when an oxidizer is applied. It results in a blue-white to yellow-green luminescence if blood is present.
What is the most common presumptive test for semen?
The most common presumptive test for semen is Brentamine Fast Blue B. It involves this chemical being applied to the sample on an alpha-naphthyl phosphate substrate. An intense purple colour will show if there is semen present on the sample.
What does ELISA stand for?
ELISA stands for enzyme-linked immunosorbent assay which is used to detect p30 (prostate specific antigen) levels (at really low levels).
How long can motile sperm survive in the vagina?
Motile sperm can survive in the vagina for about 3 hours, ranging from 1-8h. They survive longer in the cervix, for up to several days in some cases.
Name the presumptive test for saliva.
The presumptive test for saliva is called the radial diffusion test.
What’s the difference between a wipe and a swipe?
A wipe stain is created when an object moves through a pre-existing bloodstain. A swipe stain is the transfer of blood onto a target by a moving object itself that is bloodstained.
What is a cast-off stain?
A cast-off stain is the result of blood being flung or projected from a bloody object in motion or one that stops suddenly. They are linear and reflect the position of the person moving the bloody object.
How is point-of-origin determined?
Point-of-origin is determined by looking at the paths that converge from the point. The more paths converge to this point, the more confidence we have that it is the point of origin. Note that paths can sometimes cross separately from the point of origin. Visual aids are available to assist in determining the origin.
