Serological tests By: Deshanie Govender Primary serological tests: (Marker techniques) e.g. 1. – – – Classification of antigenEnzyme linked immuono sorben assay (ELISA) antibody interactions: Immuno flurescent antibody technique (IFAT) Radio immuno assay (RIA) Secondary serological tests: e.g. 2. – Agglutination tests – Complement fixation tests (CFT) – Precipitation tests – Serum neutralization tests (SNT) – Toxin-antitoxin test Agglutination tests: 1. Agglutination/Hemagglutination The reaction of an antibody with the antigen can be detected by agglutination (clumping) of the antigen. The general term agglutinin is used to describe antibodies that agglutinate antigens. When the antigen is an erythrocyte the term heamagglutination is used. a. Qualitative agglutination test Agglutination tests can be used in a qualitative manner to evaluate for the presence of an antigen or an antibody. The antibody is mixed with the particulate antigen and a positive test is indicated by the agglutination of the particulate antigen. For example, a patient's red blood cells can be mixed with antibody to a blood group antigen to determine a person's blood type. In a second example, a patient's serum is mixed with red blood cells of a known blood type to assay for the presence of antibodies to that blood type in the patient's serum. b. Quantitative agglutination test Agglutination tests can also be used to measure the level of antibodies to particulate antigens. In this test, serial dilutions are made of a sample to be tested for antibody and then a fixed number of red blood cells or bacteria or other such particulate antigen is added. 2-Passive hemagglutination: The agglutination test only works with particulate antigens. However, it is possible to coat erythrocytes with a soluble antigen and use the coated red blood cells in an agglutination test for antibody to the soluble antigen. This is called passive hemagglutination. The test is performed just like the agglutination test. Applications include detection of antibodies to soluble antigens and detection of antibodies to viral antigens. Blood Spatter Blood Spatter = 2 or more droplets of blood used to reconstruct a series of events surrounding a violent event. BSA can determine Mechanism that created the stains Direction a blood droplet was traveling Point/Area of origin Type of object used in attack Minimum number of blows Positioning of the victim, suspect and objects during events Sequence of events ANGLE OF IMPACT 1) Passive Drops EXTRA ROUGH SURFACE SMOOTH SURFACE ROUGH SURFACE Low Velocity Impact (LVI) Blood Spatter size: large (4 mm +) Impact velocity: up. to 5 feet/sec Example cause: gravity Medium Velocity Impact (MVI) B.S. size: Medium (1 - 4 mm) Impact velocity (5 to. 25 feet/sec) Example cause: car accident / blunt force trauma High Velocity Impact (HVI) B.S. size: (1 mm or smaller) Mist like appearance. Impact velocity: 100 feet/sec and greater. Example cause: gunshot Arterial Spurting Bloodstain pattern(s) resulting from blood exiting the body under pressure from a breached artery Determining angles of impact Angle of impact = direction blood drop(s) was/were traveling Blood droplets in freefall have the shape of a sphere. Droplets striking surfaces make it possible to determine the angle at which the droplet struck the surface.