Is she cheating?
Principle of Action
Description of the Kit
Can this kit be used to test a man?
Materials supplied in the kit
How old can the stain be?
Are all stains semen?
Will the AP test strips leave stains?
Materials not supplied but required
Simple procedure
Possible complications
Additional information

Do you suspect that your spouse is being unfaithful?  If so, the InSite® Semen Detection Kit can provide evidence of her infidelity.  This kit has two components:  acid phosphatase (AP) test strips and prostate specific antigen (PSA) test strips, which work together to provide evidence of semen on a woman's undergarment.

This kit is designed to be easy to use and yields instant results with the AP test strips, or results after 10 minutes with the more sensitive PSA test.  It will detect traces of semen on a woman's undergarment which has been discharged after sexual intercourse, and up to 36 hours later.

The InSite Semen Detection Kit contains 10 AP test strips in a resealable pouch with desiccant, 10 PSA test strips in sealed individual pouches and a 5-mL dropper.  The AP strips can detect semen down to a 1/2000 dilution, while 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.

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], which forms the principle of the AP test in the InSite kit.  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, and therefore the latter was chosen for inclusion 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.

Semen may be detected on women's undergarments which has been discharged up to 17 hours after intercourse with the AP test strips, and up to 36 hours after intercourse with the PSA test strips.  The AP test is presumptive, and a positive result should always be followed by a PSA test for confirmation of the presence of semen.
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. 
PSA has been detected in semen stains on garments over 30 years old [Ref. 7].
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.

There is a possibility the azo dyestuff in the AP test strip will stain a test garment.  Therefore, if you are concerned about this, you should first wet the garment with a few drops of water, press a cotton-tipped swab against the wetted area and then press the swab against the AP strip. This method ensures your spouse will not be any wiser to the fact you are testing her garments.

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.

  • 10 AP test strips in a resealable pouch with desiccant

  • 10 PSA test strips in individual sealed pouches

  • 5-mL dropper

  • Instruction sheet

  • Distilled or deionized water

  • Latex gloves (available from drug store)

  • Coffee cup

  1. AP test:  place 5-10 drops of water on a suspect area of the garment.  Press an AP strip against it.  A color change to bright purple within the first 60 seconds is a POSITIVE test.  If the test is POSITIVE, proceed with a PSA test to confirm the presence of semen.  If the test is NEGATIVE, but you are suspicious there might be a trace of semen on the garment, do the PSA test anyway.

  2. PSA test Place 15 mL of water in a coffee cup using the supplied dropper.  Then, manually extract the suspect area (i.e. crotch) of the garment by repeatedly allowing water to soak in, then pressing it out.  Finally, wring out the garment into the cup.  Place a PSA test strip into the cup and wait 10 minutes.  Then, take the test strip out and lay it on a clean dry surface.  Read the test strip after 10 minutes.  A POSITIVE test is indicated by two lines as shown below.  A strongly positive test will be clearly visible within two minutes, while a weakly positive test may take the entire 20 minutes to become evident.

    If you are testing absorptive pads (used during a woman's menstrual period), then place 25 mL of water into the coffee cup (for a full pad) or 10 mL for a mini-pad, and repeatedly extract the pad manually.  Then, wring out the pad into the cup and discard it.  Do the PSA test as usual.

  • Condoms.  If your spouse and her lover are using condoms, there probably will not be any semen to test.  In this case, you must use other means of surveillance.
  • Vasectomy.  A vasectomy will NOT affect the outcome of the test, because a man still produces semen.  PSA and AP both come from the prostate gland, which remains intact after a vasectomy.
  • Menstrual period.  A woman's menstrual period does not interfere with the detection of PSA by the strips.
  • Variability.  Sometimes the PSA test goes negative within 24 hours after intercourse, and sometimes it stays positive for over 36 hours, even in the same woman only days apart.  This variability may be due to pH changes in the vagina, among other factors.  The vaginal pH is usually around 4, which is low enough to denature proteins like PSA within 48 hours and render them undetectable.  The rate of production and quality of cervical mucus also varies within the menstrual cycle.  Because of this natural variability, the item to be tested should have been worn as close as possible to the time of suspected intercourse.
  • False positives.  Vaginal fluid contains small amounts of acid phosphatase, and may turn an AP test strip blue given enough time.  Therefore, it is important to read this test within 60 seconds, and if it is POSITIVE, perform a PSA test to confirm the presence of semen.
More information is available in our White Papers section.
Read the Instruction Sheet in English, Portuguese, Spanish, Russian, French, German or Arabic .
Watch the Instructional Video:  in Quicktime® or Windows Media®.
  1. Hooft, P. J. and van de Voorde, H. P.  American Journal of Forensic Medicine & Pathology 1997, 18, 45-49.

  2. Pilch, B. and Mann, M. Genome Biology 2006, 7:R40.

  3. Tanaka, M. et al  FEBS Letters 2004, 571, 197-204.

  4. Babson, A. L. et al, Am. J. Clin. Path. 1959, 32, pp. 88-91.

  5. Owen, D. H. and Katz, D. F. Journal of Andrology 2005, 26, 459-469.

  6. Hooft, P.; van de Voorde, H. and van Dijck, P. Forensic Science International 1992, 53, 131-133.

  7. SERATEC GmbH.  "PSA in Body Fluids--an overview for users of the SERATEC PSA SEMIQUANT Tests."

  8. Beckmann, C. R. B. et al.  "Obstetrics and Gynecology, Second Edition";  Williams & Wilkins:  Baltimore, 1995; p. 294.

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