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Am Fam Physician. 2000;61(10):3123-3124

Many substances, including semen, have been reported to fluoresce under examination with a Wood's lamp. Consequently, use of the Wood's lamp has been recommended as a method of identifying semen in a sexual assault examination. Santucci and associates question whether other commonly used substances might also fluoresce and be confused with semen. They also tested whether the Wood's lamp was, in fact, a useful screening device for detecting semen.

Forty-one physicians completed questionnaires that collected information about their length of practice and the frequency of performing sexual assault examinations. Almost one half (46 percent) of the physicians reported that they sometimes or always used a Wood's lamp during sexual assault examinations.

Each physician was then asked to identify semen on cotton swatches by using a Wood's lamp. The study took place in a darkened room with a Wood's lamp with a wavelength of approximately 360 nm. Twenty-nine different samples of semen and 13 other substances had been applied to cotton fabric and allowed to air dry. The other substances included soap, toothpaste, hand cream, saliva, bacitracin zinc, Surgilube, spermicide and A&D ointment.

Only one of the physicians was able to correctly identify the semen. The substances most commonly mistaken for semen were A&D ointment, Surgilube, Barrier cream and bacitracin ointment. Most of the semen samples were analyzed within 12 hours; none of the semen samples was found to fluoresce under the Wood's lamp. A review of the literature from companies that supply Wood's lamps showed that all recommended a standard Wood's lamp (as used in this study) for identification of semen during an assault examination. The researchers found that semen actually is more likely to fluoresce at a wavelength of about 490 nm (rather than the 360 nm of the standard Wood's lamp). The authors conclude that a standard Wood's lamp was not helpful in distinguishing semen from other substances that might be present during a sexual assault examination. It may be that a lamp with a longer wavelength would help screen for the presence of semen; further studies are needed.

editor's note: Many reviews of ways to perform a sexual assault examination recommend using a Wood's lamp to check for the presence of semen. This study convincingly shows that this practice, at least with a standard Wood's lamp, should be abandoned.—g.b.h.

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