Detecting and identifying body fluids at a crime scene can provide essential information about a crime or incident and the people involved. Like other physical flood forensic experts or scientists may be asked to recognize the presence of urine in cases such as harassment, rape or murder.
Urine is a difficult bodily fluid to detect due to the sensitivity of available tests and low positive results. The nature of the fluid causes it to dilate and thin out on the surfaces of the fabric, and it makes it harder to find. Smell may be an indicator, but it will cover a whole thing and will not be local to the area with stains.
Composition of Urine
- It is mainly composed of water with urea, organic salts, proteins, hormones and a huge range of metabolites. It generally contains about 60 parts of water and 40 parts of solid materials.
- Urea is an organic compound that is found in higher concentrations in urine than any body fluid.
- Creatinine is another organic compound present in high concentrations in urine.
- Unusually it may contain sugar albumin by pigment in case of jaundice as abnormal amount of one and other of its normal component.
Visual/ Physical Examination
Following are considered as important attributes in this initial examination:
- Specific Gravity
- Generally specific gravity is measured by Refractometer.
- The specific gravity of urine is higher than water.
- The specific gravity of urine is 1.06 to 1.0 whereas water specific gravity is 1.
4.5 – 8.5
(It is indicator of diet.)
Examination For Urine
GEE’s Methods or Urea Nitrate Crystals Test
In This Method Colorless 4 To 6 Sided Rhombic Shape Urea Nitrate Crystals Formed If Positive After Adding A Drop Of Conc. HNO3.
The DMAC (para-dimethylaminocinnamaldehyde)test is perhaps one of the most common methods for detecting urine based on the presence of urea, producing a pink or magenta color if positive.
Stain Treated With Resorcinol Reagent And CuBr2 Will Produced RedColour Which Show Presence Of Indican.
In this test chromatographic paper of stain treated with 2N NaOH followed by a drop of picric acid produced Orange/Red/Brown colour if positive.
Creatinine is another compound found in high concentrations in urine, thus a number of tests have attempted to utilise this for urine identification tests. The Jaffe test utilises picric acid which, in the presence of creatinine, forms a red compound known as creatinine picrate. The colour change is proportional to the concentration of creatinine present.
The Salkowski Test Produces A Blue Colour In The Presence Of Urine Via A Reaction Between Sodium Nitroprusside And Creatinine When Heated.
RSID (Rapid Stain Identification Series)
The immunological RSID test has also been developed for the detection of urine, based on the presence of a urinary protein known as the Tamm-Horsfall protein.