Serology And Blood Stain Pattern Analysis

Question 1

Define the terms ‘angle of impact’ and ‘direction angle’

Answer 1

ANGLE OF IMPACT - acute angle created by the intercept of the target with the droplets vector

DIRECTION ANGLE - angle between the longest axis of the stain and a standard reference point

Question 2

Define the terms ‘forward’ and ‘back’ spatter

Answer 2

FORWARD - blood droplets projected away from the item creating impact

BACK - droplets being projected towards the item (lighter and smaller stains)

Question 3

Define the terms ‘passive’, ‘transfer’ and ‘impact bloodstains’

Answer 3

PASSIVE - clots, drops, flows and pooling

TRANSFER - wipes, swipes, pattern transfers and general contact bloodstains

IMPACT - spatter, gushes, splashes and cast-off stains

Question 4

What confirmatory test is used for detecting semen?

Answer 4

Christmas tree stain

Question 5

What presumptive test is used for detecting semen?

Answer 5

BRENTAMINE FAST BLUE B

1. Filter paper or swab moistened with sterile water and applied to questioned stain
2. Reagent added = if intense purple colour seen then it’s positive

Question 6

Describe the Ouchterlony test

Answer 6

1. Agarose gel with circular pattern of 6 wells and one centre well
2. Antihuman serum placed in centre well and human control in every other well = diffuse
3. Human controls test positive with a diffusion line is unknown tests positive the line extends between sample of known

Question 7

How is human antiserum produced?

Answer 7

1. Injecting rabbits with human blood
2. Rabbits immune system reacts to foreign blood producing antibodies to neutralise it
3. Serum isolated and drawn = used to detect blood

Question 8

Describe the confirmatory test to detect blood

Answer 8

TAKAYAMA TEST

1. Small sample of presumptive stain onto a coverslip and then heated where pyridine in alkaline conditions is added in presence of a reducing sugar
2. Salmon coloured crystals form in blood

Question 9

Describe the 3 presumptive tests used to detect blood

Answer 9

PHENOLPHTHALEIN
- testing chemical added to suspended stain and hydrogen peroxide used as an oxidant for haemoglobin = colour change from colourless to pink

LUMINOL
- testing chemical sprayed onto surfaces and observed under alternate light source for glowing = reacts with haemoglobin when oxidant is present = blue-white to yellow-green luminescence

FLUORESCEIN
- like luminescence HOWEVER contains a thickener = able to stick to difficult surfaces and produces fluorescence

Question 10

Describe the ABO blood system

Answer 10

TYPE A
- RBC has A antigens and B antibodies (not A)

TYPE B
- RBC has B antigens and A antibodies (not B)

TYPE AB
- RBC has A and B antigens and no A and B antibodies

TYPE O
- RBC has NEITHER A or B antigens and both A and B antibodies

Question 11

Describe the components that make up blood

Answer 11

BLOOD - tissue composed of several types of cells in a matrix called plasma

ERYTHROCYTES - (RBC) transports oxygen and carbon dioxide through the body via haemoglobin and the circulatory system

LEUKOCYTES - (WBC) active in immune system

Question 12

Define the terms ‘Presumptive’ and ‘Confirmatory’ test

Answer 12

PRESUMPTIVE - highly sensitive to but not specific to a particular substance

CONFIRMATORY - test positive for a substance in question and only that substance