Semen Analysis

Semen Analysis

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Seminal fluid (semen) is a complex mixture of secretions from at least four male urogenital glands.

    Seminal vesicle                 60%
    Prostate gland                 30%
    Epididymis & Bulbourethral gland                 10%

An average male ejaculate measures around 3.5 millimeters containing 10-50 million sperm cells per millimeter. This number varies with the age, medical conditions, genetic background, and habits such as smoking and use of drugs.

The identification of semen is of great value in medicolegal practice like alleged rape cases or sexual assaults. The primary aim of semen forensic analysis is to sample and examine smears or other biological material taken from the assailant, the victim or stains found on clothes and/or other evidence at the crime scene. In cases of sexual assault, two steps are required: locate the stain and prove its identity. Semen analysis can also help in successfully linking semen to a suspect through DNA typing.

Presumptive Tests for Semen

    1. Visual and Alternate Light source (ALS) – Semen can be detected with the naked eye in clothing and undergarments or through the use of ALS such as ultraviolet light.

    2. Acid Phosphatase (AP) test – The male prostate gland produces and secretes high amounts of acid phosphatase (AP), an enzyme, in the semen. Using standard chemical reactions, laboratories can analyse a given stain for the presence of this enzyme. In the presence of certain stains, AP will produce a dark purple color in less than a minute.

    3. Prostate Specific Antigen (PSA) – Prostate specific antigen also known as PSA or P30 can be detected in semen. PSA is produced in high amounts by the male prostate gland but can also be found in very small amounts in fecal matter and breast milk.

Confirmatory Tests for Semen:

    1. The Christmas Tree Stain
    The Chridtmas Tree Stain is a positive identification of sperm cells. Two reagents are used consecutively to produce this distinctive stain: Picroindigocarmine stains and Nuclear Fast Red. The first stain stains the neck and tail of the sperm cell in green and blue whereas the latter one stains the sperm head and acrosomal cap with red and pink, respectively.

    2. RSID-Semen Strip Test
    This test provides sensitivity and specificity to human semen. Similar to pregnancy test strip, the RSID-semen test identifies the presence of the seminal vesicle-specific antigen. This antigen is unique to semen and thus, there is no cross reactivity with other body fluids.

Collecting DNA Evidence with Semen

1. Absorb suspected liquid semen on a clean cotton swab. Air-dry the swab and pack in a clean envelope with sealed corners.

2. Submit small and dry suspected semen-stained objects to the laboratory. Pack in clean envelope with sealed corners to prevent stain removal.

    a. Define the investigator’s role
    b. Ensure scene integrity
    c. Conduct the scene walkthrough
    d. Secure required resources

3. Documenting the scene

    a. Develop written documentation
    b. Photograph and videotape the scene
    c. Locate and interview victims and witnesses

4. Processing evidence at the scene

    a. Assemble the evidence processing team
    b. Organize evidence processing
    c. Control scene contamination
    d. Identify, collect, preserve, inventory, package, and transport evidence

5. Completing and recording the scene investigation

    a. Make sure all investigative steps are documented
    b. Ensure that scene processing is complete
    c. Release the scene
    d. Submit reports

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It is a capital mistake to theorize before you have all the evidence. It Biases the Judgement

Sherlock Holmes