Laboratorio de Química Forense, Instituto de Servicios Periciales, Procuraduría General de Justicia del Estado de México, 50090 Toluca, Mexico.
Forensic Sci Int. 2011 Mar 20;206(1-3):111-8. doi: 10.1016/j.forsciint.2010.07.012. Epub 2010 Aug 9.
In the forensic laboratory the biological analyses for rape investigation commonly include vaginal swabs as sample material combined to biochemical tests including sperm cytology (SC) and detection of acid phosphatase activity (AP) and prostate-specific antigen (PSA, p30) for the conclusive identification of semen components. Most reports comparing these tests relied on analysis of semen samples or donor swabs taken under controlled conditions; however their individual or combined efficacy under real live sampling conditions in different laboratories is largely unknown. We carried out SC, APA and PSA analyses in vaginal swabs collected from casework rapes submitted to Mexican Forensic Laboratories at Texcoco and Toluca. On the basis of positive and negative results from each assay and sample, data were classified into eight categories (I-VIII) and compared with those obtained in the two only similar studies reported in Toronto, Canada and Hong Kong, China. SC and APA assays had the higher overall positivity in Toluca and Texcoco samples respectively and otherwise PSA had a lower but very similar positivity between these two laboratories. When compared to the previous studies some similarities were found, namely similar frequencies (at a ratio of approximately 1 out of 3) of samples being positive or negative by all techniques (Categories I and VI respectively) and a comparable overall positivity of APA and SC but higher than that of PSA. Indeed the combined results of using SC, APA and PSA tests was considered as conclusive for semen detection from approximately 1 out of 3 cases (Category I) to approximately 1 out of 2 cases in a scenario where at least SC is positive, strongly presumptive in 2 out of 3 cases (with at least one test positive) and the remainder 1 out of 3 cases (Category VI) suggested absence of semen. By determining Y-STR polymorphisms (12-loci) in additional samples obtained at Toluca laboratory, complete DNA profiles were determined from all Category I samples, none marker was detected from all Category VI samples and mostly partial profiles were obtained from samples of other categories. These observations give an overview on the variability in efficacy of each test performed at different laboratories and provide a general notion about the in praxis contribution of SC, APA and PSA tests for further DNA typing in the forensic analysis of rape.
在法医实验室中，强奸案调查中的生物分析通常包括阴道拭子作为样本材料，并结合生物化学测试，包括精子细胞学（SC）和酸性磷酸酶活性（AP）以及前列腺特异性抗原（PSA，p30）的检测，以确定精液成分。大多数比较这些测试的报告都依赖于在受控条件下对精液样本或供体拭子的分析；然而，它们在不同实验室的实际现场采样条件下的单独或联合效果在很大程度上是未知的。我们对特斯科科和托卢卡的墨西哥法医实验室提交的法医强奸案件的阴道拭子进行了 SC、APA 和 PSA 分析。根据每个检测和样本的阳性和阴性结果，数据被分为八类（I-VIII），并与在加拿大多伦多和中国香港仅有的两项类似研究中获得的数据进行了比较。SC 和 APA 检测在托卢卡和特斯科科样本中的总体阳性率较高，而 PSA 在这两个实验室中的阳性率较低，但非常相似。与以前的研究相比，发现了一些相似之处，即所有技术（分别为类别 I 和 VI）的样本阳性或阴性的频率相似（约为 1/3），APA 和 SC 的总体阳性率相当，但高于 PSA。事实上，使用 SC、APA 和 PSA 测试的综合结果被认为是从大约 1/3 的情况下（类别 I）到至少 SC 阳性的情况下大约 2/3 的情况下（至少有一个测试阳性）对精液检测具有结论性的，2/3 的情况下强烈提示（至少有一个测试阳性），其余 1/3 的情况下（类别 VI）提示无精液。通过在托卢卡实验室获得的额外样本中确定 Y-STR 多态性（12 个位点），从所有类别 I 的样本中确定了完整的 DNA 图谱，从所有类别 VI 的样本中都没有检测到标志物，而其他类别的样本主要获得了部分图谱。这些观察结果概述了在不同实验室中进行的每个测试的效果的可变性，并提供了关于 SC、APA 和 PSA 测试在强奸法医分析中进一步 DNA 分型的实际贡献的一般概念。
