Ensuring specimen validity is an essential aspect of toxicological laboratories. In recent years, substituting authentic urine specimens for synthetic urine has become increasingly popular. Such synthetic urine products consist of components expected in normal urine and show physiological values for specific gravity and pH. Thus, standard specimen validity testing may fail in revealing adulteration by synthetic urine. The present study investigated three methods to distinguish authentic and synthetic urine specimens: enzymatic detection of uric acid, the commercially available Axiom Test True Synthetic Urine, and LC-MS/MS analysis of 10 endogenous biomolecules. Additionally, novel direct markers of synthetic urine were investigated. Two specimen sets were analyzed by each method. Specimen set A consisted of 8 synthetic urine products purchased from the Austrian/German market and 43 urine specimens from volunteers of known authenticity, which underwent double-blind analysis. Specimen set B consisted of 137 real urine specimens submitted for drug testing, which were selected due to initial suspicious test results in adulteration testing and reanalyzed by all three methods. Uric acid and LC-MS/MS-based endogenous biomolecule testing showed 100% sensitivity and specificity for set A. The commercial test had 87.5% sensitivity and 97.7% specificity for set A. For set B, uric acid and LC-MS/MS analysis showed almost similar results, even if uric acid was missing one presumptive authentic urine specimen according to LC-MS/MS findings. Nearly half of the synthetic urine assignments for the commercial test were presumptive false positives. New synthetic urine markers were observed for synthetic urine products from the Austrian/German market. One specimen in set B had both endogenous biomolecule pattern and synthetic urine markers suggesting urine dilution with synthetic urine. In conclusion, several analytes or methods should be used rather than one, and the most reliable results are achieved if both indirect and direct markers of urine substitution are analyzed.

中文翻译：

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用于检测合成尿液的生化测定评估和 LC-MS/MS 分析优化

确保样本有效性是毒理学实验室的一个重要方面。近年来，用真实尿液标本替代合成尿液变得越来越流行。此类合成尿液产品由正常尿液中预期的成分组成，并显示出比重和 pH 值的生理值。因此，标准样本有效性测试可能无法揭示合成尿液的掺假。本研究研究了三种区分真实尿液样本和合成尿液样本的方法：尿酸的酶检测、市售的 Axiom Test True Synthetic Urine 以及 10 种内源性生物分子的 LC-MS/MS 分析。此外，还研究了合成尿液的新型直接标记物。每种方法分析两个样本组。样本组A由从奥地利/德国市场购买的8份合成尿液产品和来自已知真实性的志愿者的43份尿液样本组成，这些样本经过了双盲分析。样本组B由137份提交药物检测的真实尿液样本组成，这些样本是由于掺假检测中最初的可疑检测结果而被选择的，并通过所有三种方法重新分析。尿酸和基于 LC-MS/MS 的内源生物分子测试显示 A 组的灵敏度和特异性为 100%。商业测试的 A 组灵敏度为 87.5%，特异性为 97.7%。B 组的尿酸和 LC-MS/MS 灵敏度为 100%。分析显示几乎相似的结果，即使根据 LC-MS/MS 结果缺少一份假定的真实尿液样本中的尿酸。商业测试的合成尿液分配中近一半是推定假阳性。在奥地利/德国市场的合成尿液产品中观察到了新的合成尿液标记。B 组中的一份样本同时具有内源性生物分子模式和合成尿液标记物，表明尿液被合成尿液稀释。总之，应该使用多种分析物或方法，而不是一种，并且如果同时分析尿液替代的间接和直接标志物，则可以获得最可靠的结果。