- The InSite Semen Detection Kit can detect traces of semen on a woman’s undergarment discharged after sexual intercourse, and up to 36 hours later.
- The InSite Kit comes with two types of test strips: (1) acid phosphatase (AP) test strips, and (2) prostate specific antigen (PSA) test strips. These two test work together to provide evidence of semen on a woman’s undergarment.
- The AP test strips can detect semen down to a 1/2000 dilution and provide instant results. The PSA test strips can detect semen to a 1/500,000 dilution and provide more sensitive results in just 10 minutes.
- The InSite Semen Detection Kit contains 15 AP test strips in a resealable pouch with desiccant, 10 PSA test strips in sealed individual pouches and a 5-mL dropper.
How It Works
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.
Semen has over 900 identified proteins 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). 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, 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). 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, 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.
Sensitivity and Accuracy
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.