Globally, the incidence of sexual assault cases, especially rape is increasing, sexual aggression is a serious social and public health issue that requires an urgent forensic medical examination. The ability to detect seminal fluid is vital in forensic cases involving sexual assaults and Sodomy crimes. Prostate specific antigen (PSA, also known as P30) is a glycoprotein produced by the prostatic gland and secreted into seminal plasma, is now accepted as a marker for detecting semen in criminal cases where detecting of sperms is of challenge such as in vasectomized or azoospermia males. It is important to note that when the PSA concentration is too high it may overwhelm this very sensitive test. The prozone or high-dose hook effect phenomenon, documented to cause false-negative assay results still remains a problem in one-step chromatographic sandwich immunoassay,immunoturbidimetric assays, and immunonephelometric assays. To detect the prozone effect, samples are often tested undiluted and after dilution, If the result on dilution is higher than for the undiluted sample, then the undiluted sample most likely exhibited the prozone effect.
Objectives: This study was design to measure the results from using three different procedure of one-step chromatographic sandwich immunoassay; short, long and dilution on forensic evidence to detect sexual assault at laboratory of forensic serology division.
Materials and methods: The material and methods were used ABA card® kits for detection prostate specific protein by use three procedures, the principle of test is one-step chromatographic sandwich immunoassay. Total sample (2870) 1910 swab (vagina, rectum, penis, Labia, perineum and mouth) and 960 different clothing were investigated for semen detection.
Results: The results show that the one-step chromatographic sandwich immunoassay method (dilution procedure) for P30 detection is useful for the identification of seminal fluid (Plasma) in sexual assault because it is evidence saved, highly sensitivity (98.8 %), specificity (100%) for human semen detection with Negative Predictive Value (0.99) and eliminate high dose hook effect Phenomena. There is uneven distribution of positive results for clothes and swabs (P =0.0005) where it is evident that it was mainly underwear for cloths and vaginal, rectal swabs were more positive.
Conclusion: The rapid membrane test (chromatographic sandwich immunoassay short method, long method) easy to implement into routine casework protocols and provides identifying seminal fluid from vasectomized and azoospermia individuals but this procedure not efficient to prevent High Dose Hook Effect Phenomena therefore this study emphasis to use dilution procedure as first choice to maintain time and evidence and elemental High Dose Hook Effect Phenomena (False Negative results).
