One of the major challenges of testing drugs of abuse is the detection of highly diluted urine samples. The ingestion of a large amount of fluid can considerably reduce the concentration of substances, possibly resulting in inaccurate drug testing. For detection, determination of urinary creatinine is a widely established procedure. In this study, results from the most popular methods, including photospectrometry (Jaffe) and liquid chromatography–tandem mass spectrometry (LC–MS/MS), have been compared regarding 327 urine abstinence control samples. Because samples with creatinine concentrations close to the cutoff of 20 mg/dL are of particular interest, only samples below 50 mg/dL were considered. Results revealed a close correlation of creatinine concentrations by both analytical methods with an R² value of 0.9005. A mean concentration difference of 3.30 ± 3.45 mg/dL was observed, indicating a moderate underestimation by the Jaffe reaction. Graphical analyses showed high accordance between both methods with only a few outliers. Due to easy handling and for economic reasons, the spectrometric method is often preferred over LC–MS/MS. For urine samples with creatinine concentrations close to the cutoff, confirmation through a second method should be performed to avoid a possible disadvantage or even severe consequences for the respective individual. It is recommended that each laboratory establishes a reliable verification method.

中文翻译：

---

验证低浓度尿样中肌酐测量的有效性——光谱法与液相色谱法——串联质谱法

检测滥用药物的主要挑战之一是检测高度稀释的尿液样本。摄入大量液体会显着降低物质的浓度，可能导致药物测试不准确。对于检测，尿肌酐的测定是一个广泛建立的程序。在本研究中，对 327 份尿禁对照样品的最流行方法的结果进行了比较，包括光谱法 (Jaffe) 和液相色谱-串联质谱法 (LC-MS/MS)。由于肌酐浓度接近 20 mg/dL 临界值的样品特别令人感兴趣，因此仅考虑低于 50 mg/dL 的样品。结果显示，两种分析方法的肌酐浓度与R ²密切相关值 0.9005。观察到 3.30 ± 3.45 mg/dL 的平均浓度差异，表明 Jaffe 反应适度低估。图形分析显示两种方法之间的高度一致性，只有少数异常值。由于易于操作和经济原因，光谱方法通常优于 LC-MS/MS。对于肌酐浓度接近临界值的尿样，应通过第二种方法进行确认，以避免对个体造成不利甚至严重后果。建议各实验室建立可靠的验证方法。