Interference of body products, food and products from daily life with the modified zinc test and the acid phosphatase test.

The modified qualitative zinc test and the qualitative acid phosphatase test were applied to a total of 1774 semen-free stains made from human body products (n = 575), food products (n = 801), beverages (n = 146), water (n = 120) and other products from daily life (n = 132), in order to assess the degree of interference of these products with the preliminary screening for semen. The zinc test gave positive results in, respectively, 2.4, 3.1, 1.4, 14.1 and 23.5% of the samples, whereas the acid phosphatase test was positive in 3, 3.3, 0, 1.7 and 0% of the samples. Given the large number of positive test results found for products which eventually may be present in stains from alleged sexual assaults, it is concluded that positive screening test results should be interpreted with great caution.