Description of the kit

The InSite Semen Detection Kit contains 15 PSA test strips in sealed individual pouches and a 5-mL dropper.  The PSA strips can detect semen to a 1/500,000 dilution.  The kit is designed to be used by men who suspect their spouse may be engaged in sexual activity outside of their relationship.  It also can be used by professional investigators, and parents concerned about whether their teenage daughters are sexually active.
 

Principle of Action

When a man has sexual intercourse with a woman, semen is deposited into the woman's vagina.  Immediately after intercourse, most of the semen flows back out, but some is retained in the vagina and slowly is discharged over a period of several days [Ref. 1].  Semen has over 900 identified proteins [Ref. 2] among which are semenogelin I and II (gel-forming proteins produced by the seminal vesicles), prostate-specific antigen (a protease which breaks down semenogelin), and acid phosphatase (which breaks down spermatozoa cell membranes) [Ref. 3]. These proteins can be identified by immunochromatographic assay, which forms the principle of the PSA test in the InSite kit. Acid phosphatase can be detected by the classic test first described by Babson [Ref. 4].  This test relies on the catalytic hydrolysis of 1-naphthyl phosphate to form 1-naphthol, which in turn reacts with an aryl diazonium salt, forming an intensely colored azo dyestuff.  In addition to proteins, semen also has unusually high concentrations of zinc (100-200 mg/L v. 1 mg/L in plasma) [Ref. 5].  Zinc acts to stabilize DNA inside spermatozoa and also may catalyze the gel-forming reaction between semenogelin I and II.  Semen may be detected by the modified zinc test of Hooft and van de Voorde [Ref. 6], but this test does not give as dramatic a color change at low dilutions as the AP test. For convenienc and economy only the PSA test is included in the InSite kit.

The semen flowing back out of a woman's vagina ("backflow") is deposited on her underwear or absorbent pad.  These items conveniently can be tested with the InSite kit.

Sensitivity

Semen may be detected on women's undergarments which has been discharged up to 36 hours after intercourse with the PSA test strips. 

Specificity

The PSA test is 100% specific for semen at a dilution of 1/500,000 or less.  This means that the probability of a false positive result is essentially zero within the first 12 hours after intercourse.  In order to be sure that the semen did not come from you, you must not have had intercourse with your spouse for at least three days prior to the test. 

How old can the stain be?

PSA has been detected in semen stains on garments over 30 years old [Ref. 7].

Are all stains semen?

NO.  Asymptomatic women produce, on the average, about 1.5 g of vaginal fluid per day, which typically leaves a white-to-beige stain [Ref. 8].  Semen stains on the other hand, are white and appear mainly just after intercourse.  The next day, discharge of residual semen may not be visible at all.

Is this a legitimate forensic test?

The PSA test can be used for the forensic detection of semen by professional investigators worldwide.  The PSA test in particular has been validated for use in forensic investigations, and the small amount of PSA present in other bodily fluids has been shown not to interfere with the detection of semen.

How does this kit compare with other test kits on the market?

The InSite^® semen detection kit has 15 test strips and is designed for long-term surveillance, since sometimes it takes awhile to catch adulteresses.  Most other kits on the market have one or two test elements, and are designed for short-term use.  In addition, the InSite kit is unique in that it has highly sensitive and specific PSA test strips.  In case of a strong stain, the PSA test is confirmatory for the presence of semen.  Finally, the PSA test procedure has been simplified so that the home user simply extracts the item to be tested in a coffee cup, and then inserts a test strip into the cup with no laboratory required.

Can this kit be used to test a man?

The InSite kit will identify semen stains on garments and other fabrics, including men's underwear.  However, there are many legitimate reasons why a man would have such stains on his undergarment--for example, nocturnal emissions.  Therefore, we question whether any inference of infidelity can be drawn solely from the presence of semen stains on the undergarment of a man.  Such evidence must be combined with other data, such as direct surveillance, in order to reach a meaningful conclusion.

Materials supplied in the kit

Possible complications