forensic serology

forensic serology

the detection, identification and typing of body fluids and secretion either in native form or as stains or residues left at a crime scene

advantages of serology over DNA

1. provides information on source of DNA

2. helps in screening of samples, fast efficient and cheap

3. helps in disputed paternity cases

serological tests

catalytic/chemical/enzymatic: blood, urine, semen, salive

crystalline tests: blood, semen

spectroscopic tests: multiple body fluid types

microscopic tests: semen

immunological tests

what is blood?

A vital fluid that carries oxygen and nutrients to cells, regulates temperature, and plays an essential role in the immune system. made of up about half liquid/plasma

Karl Landsteiner

discovered blood typing in 1901 (ABO system) comparing the blood cells to the blood serum

universal donor

o-negative

universal acceptor

AB-positive

Rh factor

determined by the presence of another antigen, the D antigen. people having the D antigen are Rh+; those not having the antigen are Rh-

presumptive blood tests:

1. luminol (bluestarTM) blue chemiluminescence

2. fluorescing: green flourescence

3. phenolphthalein or kastle meyer test: pink

4. tetramethylbenzidine (TMB): green-blue

5. leucomalachite green(LMG): green

6. hemastix strips: green

Luminol (BlueStarTM)

advantages:

1. extremely sensitive

2. does not interfere with DNA typing

disadvantages

1. not specific to blood. copper and its compounds, horseradish, and bleach also cause the solution to glow

2. chemiluminescene last for very short period of time (30 seconds)

3. require dark condition for visualization

4. probably carcinogenic

fluorescein

advantages:

1. extremely sensitive

2. does not interfere with DNA typing

3. fluorescene last longer than luminol

4. can be used even in lighted conditions

disadvantages

1. not specific to blood, copper and its compounds can also cause the solution to glow

2. require external alternate light source for visualization

3. probably carcinogenic

presumptive blood tests: combined P-TMP

P-test requires a basic environment, while TMB requires an acidic one

p-test is more specific than TMB

TMB is slightly more sensitive than P-test

positive result must come from both test

semen identification test

1. visual and alternate light test

2. acid phosphate test

presumptive tests

1. microscopic identification

2. ABA PSA card identification of P30

confirmatory

visual and alternate light tests

visual inspection:> one swab size: off-white to yellow

alternate light source: one swab size

semen fluoresce under alternate light because of flavin and choline-conjugated proteins

advantages: quick test, good for field conditions

disadvantages: not good for all semen samples as florescence get affected by heat, humidity, microorganisms etc. many other molecule fluoresce in similar way.

acid phosphatase test/ kaye’s test/ brentamine spot test

advantages

1. very quick

2. do not require visualization of semen stain first

3. can detect semen up to 500 times dilutions

disadvantages

1. sensitivity decreases with age and storage condition

2. AP also present in other body fluids