HOSA: Identification of Blood, Bloodstains, Biological Fluids and Stains

Plasma

Fluid portion of blood that contains the cellular components

Serum

Liquid portion of blood that does not clott

Erythrocytes (RBC)

Red Blood Cells, carry stuff

Leukocytes (WBC)

White Blood Cells, defend against foreign substances

Platelets

Important components in clotting

Exsanguination

Bleeding to death

Surfaces that create little spatter

Hard, smooth surfaces (Glass, smooth tile)

Surfaces that create lots of spatter

Rough surfaces (wood, concrete)

Narrow end of a blood stain

Indicates direction of travel

Area of Convergence

2D area in which blood stain originated, found by using strings to the long axis of blood stains

Area of Orgin

3D area in which blood stains originated, found by examining the angle of impact and using strings going in the direction of travel at the correct angle.

Round stains

Stains that have 90 degree angle of impact

0.5 w/l

Elliptical stain with 30 degree angle of impact

Width/Length

Ratio for discovering angle of impact

Gunshot wounds

Indicated by back and possibly front spatter and fine misting. Misting is typical of gunshots and not seen in too many other instances

Stabbing/Beating wounds

Larger spatter aroun 1-3 mm, varies depending on weapon

Castoff stains

Blood is thrown from a weapon used in a beating. These stains are typically linear and large

Splashed/ Projected Blood

Large central area with peripheral spatters. Spattering blood tends to leave narrow projections

Expirated Blood

Mist/spatter of blood due to coughing or vomiting. May contain mucous, be slightly dilute and contain air bubble. Air bubbles are a decent indication of expirated blood.

Arterial Blood

May take on many types due to the severity of the injury. ( gushing, spurting, or spraying)

Transfer Blood

Wet blood contacts an object and leaves a pattern. Requires testing to indicate the patter is correct

Color changes of blood as it ages

Red, Reddish brown, black

Blood begins to clot in

3-15 minutes

Void

Area with no blood on it while surrounded by blood. Indicates that an object has been moved

Passive Blood Stains

Caused by transfer of blood from an area, flow patters, and saturation stains

Active Blood Stains

Caused by impact, arterial spurts, expirated and castoff stains

ABO

Classification of blood types based on the reactions of antibodies and antigens

Serology

The laboratory study of body fluids using specific antigen and serum antibody reactions

Agglutination

Process of red blood cells clumping together in response to an antibody

Precipitin Test

Test that distinguishes between human and animal blood

Benzidine test

A regent once widely used as a presumptive test for blood in feces. Involved using ethanol/acetic acid solutions which turned blue when the reagent and blood were added.

Hemastix test

Commercial test strip that can be used as a presumptive test for blood. Designed to detect blood in urine but works well in forensic settings

Phenolphthalein Test

A presumptive test for blood that turns pink when blood is added to the reagent.

Luminol/Flourescein tests

Presumptive blood test based on chemical reactions that cause light to be emitted from the blood stain

Crystal tests

A type of presumptive test in which a positive result is the formation of a solid crystalline substance

Seminal Acid Phosphate

Enzyme found in abundance in seminal fluid. Commonly tests for when testing for semen.

Alpha-amylase

Enzyme found in saliva that is the basis for presumptive tests for that fluid. (Starch-iodide tests are common)

Azostix

Test used forensically to detect urine. Commercially used to detect blood in urine. (Urine tests are inaccurate and not common in forensic science)

Periodic acid-Schiff reagent

Presumptive test for the presence of vaginal material, glycogenated cells are stained bright magenta.

A black colored stomach mucosa is associated with...

Cyanide

Sex can be determined by examining hair for what?

Barr bodies (condensed 2nd X chromosome)

Branching tree on the front of the chest is usually caused by?

Lightning

Which organ is least likely to be injured by a blast wave?

Liver