SEMEN ON PANTIES - HISTORY OF SEMEN DETECTIONS

                       

Prostate Specific Antigen (PSA) Semen Detection Testing

  • Prostate-specific antigen (PSA)  is a glycoprotein produced in the prostate and secreted into the seminal fluid. PSA is one of the major proteins in seminal fluid with concentrations of 0.2 to 3.0 mg/ml. Its main function is to liquefy the seminal fluid. This high amount makes PSA a useful marker in forensic science for the detection of even small amounts of seminal fluid. 

 

  • The advantages of a PSA determination are:  

    • Prostate-specific antigen (PSA) or p30 is an accepted marker for detecting semen in criminal cases.

    • The PSA test is not presumptive like the Acid Phosphatase (AP) Semen Detection Test.

    • The detection of PSA is possible in cases where no spermatozoa can be found (for example vasectomized or azoospermic men. 

    • PSA can be recovered at detectable concentrations in 30 year old semen stains (reference).

    • Semen samples can show positive PSA results even at a dilution factor of 1:200,000 (ref Sato)

    • PSA is detectable in post-ejaculate urine and male urine from adult men and can be detected in urine of eleven year old boys (ref Sato).

     

 

  • Most laboratories use a simple PSA cartridge in lieu of early methods of p30 detection which are:

    • Ouchterlony double diffusion

    • Rocket Immunoelectrophoresis

    • ELISA (still used in many labs)

    • Crossover Electrophoresis

    • Radial Immunodiffusion

 

  • The Prostate Specific Antigen (PSA) Test Cartridge is based upon the following principals.
    • The membrane contains two monoclonal murine anti-PSA antibodies as active compounds. One of these antibodies is immobilized at the test region on the membrane. The upstream control region and the region of the internal standard (between control and test region) contain immobilized polyclonal goat anti-mouse antibodies. The amount of antibody at the internal standard is adjusted to a color intensity of the line, which is equal to the color intensity of the test line at a PSA concentration of 4 ng/mL. A glass fiber pad downstream of the
      membrane is used for sample loading and transmission to a second fiber pad with the dried and gold labeled second monclonal murine anti-PSA antibody.
    • PSA at the sample will bind to the re-mobilized gold-labeled antibody and form a PSA-gold-labeled-anti-PSA-antibody-complex. Through the capillary effect of the membrane, the reaction mixture including the complex is carried upwards with the fluid. In any case the colored gold labeled anti-PSA-antibody will bind to the anti-mouse-antibody at the control region and the region of the internal standard thus developing two red lines (one at the control region ant one at the region of the internal standard). These two lines are independent of the existence of PSA at the sample and indicate only the correct execution of the test. 
    • If the sample contains PSA the PSA-gold-labeled anti-PSA-antibody complex will bind to the immobilized monoclonal antibody of the test region that recognizes another epitope on the PSA molecule. The binding is indicated by the formation of an additional line. Thus a PSA positive sample will show three colored lines in the result well. The line in the middle (internal standard) correlates with an amount of 4 ng/ml PSA. In some cases it might be helpful to estimate the amount of PSA in the sample by comparison of the result line with the internal standard line.

 

  • These raw cartridges or complete test kits can be purchased in quantities at ProstateSpecificAntigen.net.  Individual test kits can be purchased directly from this website at this link.