Urine as a Biological Evidence In Forensic Science

Urine is the by product of the cellular metabolism in humans. Urine is yellow-straw coloured fluid produced by the process of urination. It is excreted out from the body by an opening called urethra. It follows a pathway from kidney to urinary bladder through ureters.

On an average urine production is around 1.4 Litres per day by per person. It depends from person to person on the various fcactors like weight , health, state of hydration and environmental factors.

 CONSTITUENTS OF URINE

Urine is an aqueous solution of greater than 95% water, with a minimum of these remaining constituents, in order of decreasing concentration:

• Urea 9.3 g/L
• Chloride 1.87 g/L
• Sodium 1.17 g/L
• Potassium 0.750 g/L
• Creatinine 0.670 g/L
• Other dissolved ions, inorganic and organic compounds (proteins, hormones, metabolites)

Abnormal Constituents of Urine

Many a times tests are used in analyzing the urine in order to determine, whether it contains abnormal substances indicative of diseases or illegal use of some drugs . Usually abnormal substances that are present in the urine are :

• Proteinuria—Protein content in urine, often due to leaky or damaged glomeruli.
• Oliguria—An abnormally small amount of urine, often due to shock or kidney damage.
• Polyuria—An abnormally large amount of urine, often caused by diabetes.
• Dysuria—Painful or uncomfortable urination, often from urinary tract infections.
• Hematuria—Red blood cells in urine, from infection or injury.
• Glycosuria—Glucose in urine, due to excess plasma glucose in diabetes.

COLOR OF URINE

It is mainly transparent or ranges from colorless to amber or pale yellow. The color is due to UROBILIN which is final waste product. Its formed by breakdown of hemoglobin during the destruction of aging of blood cells. There are few  conditions in which the color of urine variates from the normal. Some of them are :

• Dark yellow indicates the dehydration
• Light orange due to removal of excess of B vitamins.
• Urine with blood is termed as hematuria which is caused due to medical conditions
• Dark orange to brown  is due to jaundice
• Pinkish urine is due to consumption of beets.

EXAMINATION OF URINE

1. Physical Examination

2. Visual Examination

A suspected urine stain may fluoresce pale yellow or pale blue when viewed under long and short wave UV light.  Safety eyeglasses, which absorb ultraviolet radiation, must be worn when viewing material for fluorescence.

3. Microscopic Analysis

Normal Urine – White blood cells in very less quantity. Bacteria, yeast cells , parasites absent.

Abnormal Urine – Red blood cells in the urine indicate kidney or bladder injury, kidney stones, a Urinary Tract Infection (UTI).

4. CHEMICAL TEST

Detection of urine stain is based on detection its constituents like urea, amines, phosphates , sulphates, etc.

• Urea in a suspected ‘urine’ stain can be detected with urease- bromothymol paper. If present, urea would be enzymatically decomposed to ammonia and carbondioxide by urease. This liberated ammonia will shift the pH. It will change the color from yellow to blue.

5. CONFIRMATORY TEST

A. CREATININE TEST

This test is also called Jaffé colour test. In this test, picric acid is used to convert creatinine under alkaline condition to form creatinine picrate. Picric acid is strong oxidising agent. Creatinine is getting oxidised which is produced by muscle metabolism. Amount of urine excreted in urine is proportional to muscle mass of individual.

Procedure

1. Extract the stained material and blank sample.

2. Put one drop of picric acid in both the samples.

3. Add 5% of sodium hydroxide solution in the stain.

4. Observe the colour change. The blank sample turns yellow colour and the stained sample turns red to brown colour change.

The red to orange to brown  colour crystal indicates the presence of creatinine in the urine.

B. TEST FOR UREA NITRATE

Urea nitrate is produced in one step by reaction of urea with nitric acid. This crystal test indicates the presence of urea in the given sample.

Procedure :

• Take the drop of sample on the galss slide.
• Put 2-3 drops of conc. nitric acid. Prevent overflow.
• Cover the slide with coverslip.
• Observe the slide under the microscope.

Observations:

Appearance of rhombohedral stacked crystals of urea nitrate which are colorless or transparent indicates the presence of urine in the sample.

C. Detection of Indican

1 ml of resorcinol reagent is added to the small quantity of the extracted stain then the 1ml of cupric bromide solution is added mixed and whole mixture is extracted with amylacetate. The red colour of the crystal indicates the presence of Indican.

D. UA/UN Ratio

Uric Acid and Urea Nitrogen ratio multiplied by 20 in human urinary stain is between 1 and 4, in other stains and animal urine its <1 or >4.

E. Tamm Horsfall protein or Uromodulin

Urine contains a glycoprotein called Tamm Horsfall protein, produced exclusively by renal tubular epithelial cells within the distal loop of Henle. This can be detected by Radioimmunoassay.

THIN LAYER CHROMATOGRAPHY

Various methods for the detection of urea for urine stain identification have been described above.  Thin-layer chromatography is also used to detect both urea and creatinine in an effort to make the test more specific for urine, and also additional components of urine on TLC plates can be used for the same purpose.

URINE DRUG TESTING

Urine is very frequently tested for the presence of drug in a person’s system. Urine testing is evasive, quick , cost effective and can be screened for metabolites of parent drug. Drugs of the category glucocorticosteroids, beta blockers, stimulants, diuretics, barbiturates can be detected in urine.

FORENSIC IMPORTANCE OF URINE AS AN EVIDENCE

It can be found in the cases of Strangulation, violent cases, poisoning cases, sexual assault etc. It can be used to analyse the presence of drugs, proteins , alcohol and poisons.

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