Fraser Albert D, Zamecnik Jiri
Department of Pathology and Laboratory Medicine, Queen Elizabeth II Health Sciences Centre, Halifax, Nova Scotia, Canada.
Ther Drug Monit. 2003 Dec;25(6):723-7. doi: 10.1097/00007691-200312000-00011.
Many clinical and forensic toxicology laboratories establish criteria for identifying a random urine specimen submitted for drug screening as being "normally concentrated" or "dilute" by incorporating creatinine analysis and/or specific gravity measurement into their testing protocols. The objective of this study is to describe the importance of urine creatinine analysis and specific gravity measurements in the Correctional Service of Canada (CSC) drug-testing program. The CSC program uses the Substance Abuse and Mental Health Services Administration (SAMHSA) creatinine cutoff value (20 mg/dL) mandated for workplace drug testing in the United States. In the CSC program, urine specimens must have a creatinine concentration <20 mg/dL and specific gravity value </=1.003 to be considered dilute. The CSC program also incorporates lower drug/drug metabolite screening and confirmation cutoff values (dilution protocol) for specimens that are administratively defined as dilute. Seventy-nine hundred and twelve urine specimens from 2000 to 2002 (6.8% of total workload) were defined as dilute. Twenty-six percent of all dilute specimens (n = 2054) screened positive for one or more drugs using the SAMHSA cutoff values. The screening-negative dilute specimens were taken through the dilution protocol scheme with lower screening cutoff values and confirmation cutoff concentrations at the lower limits of quantification (LLOQ) for each method. Over 1100 of the 5858 dilute urine specimens (18.8%) confirmed positive for one or more drugs in 2000 to 2002 when taken through the dilution protocol scheme. CSC workload is separated based on whether specimens are referred from institutions or from community settings (such as parolee programs). The positive rate for dilute specimens averaged 18.2% from CSC institutions and 22.3% from specimens collected from parolee specimens in 2000 to 2002. The drugs most often confirmed in dilute specimens from institutions were cannabinoids (annual positive rate ranged from 13.7 to 18%) and codeine and/or morphine (ranged from 0.2 to 2.8%). The drugs most often confirmed in dilute urine specimens from community settings in 2000-2002 were cannabinoids (annual positive rate ranged from 10.3 to 12.5%) and cocaine metabolite (ranged from 6.6 to 10.3%). In conclusion, one can reduce the false-negative rate for drugs of abuse in urine drug testing programs by incorporating lower screening and confirmation cutoff (eg, LLOQ) concentrations for dilute specimens that screen negative for drugs of abuse when using the SAMHSA mandated screening and confirmation cutoff concentrations.
许多临床和法医毒理学实验室通过将肌酐分析和/或比重测量纳入其检测方案，来制定标准，以确定提交进行药物筛查的随机尿液样本是“正常浓缩”还是“稀释”。本研究的目的是描述尿液肌酐分析和比重测量在加拿大惩教署（CSC）药物检测项目中的重要性。CSC项目采用了美国物质滥用和精神健康服务管理局（SAMHSA）规定的用于工作场所药物检测的肌酐临界值（20mg/dL）。在CSC项目中，尿液样本的肌酐浓度必须<20mg/dL且比重值≤1.003才能被视为稀释样本。CSC项目还针对行政定义为稀释的样本采用了更低的药物/药物代谢物筛查和确证临界值（稀释方案）。2000年至2002年的7912份尿液样本（占总工作量的6.8%）被定义为稀释样本。使用SAMHSA临界值时，所有稀释样本中有26%（n = 2054）对一种或多种药物筛查呈阳性。筛查为阴性的稀释样本按照稀释方案进行处理，采用每种方法定量下限（LLOQ）处更低的筛查临界值和确证临界浓度。在2000年至2002年，5858份稀释尿液样本中有超过1100份（18.8%）按照稀释方案处理后对一种或多种药物确证呈阳性。CSC的工作量根据样本是来自机构还是社区环境（如假释人员项目）进行区分。2000年至2002年，来自CSC机构的稀释样本阳性率平均为18.2%，来自假释人员样本的阳性率为22.3%。机构稀释样本中最常被确证的药物是大麻素（年阳性率在13.7%至18%之间）以及可待因和/或吗啡（在0.2%至2.8%之间）。2000 - 2002年社区环境下稀释尿液样本中最常被确证的药物是大麻素（年阳性率在10.3%至12.5%之间）以及可卡因代谢物（在6.6%至10.3%之间）。总之，在使用SAMHSA规定的筛查和确证临界浓度时，对于滥用药物筛查呈阴性的稀释样本，通过采用更低的筛查和确证临界值（如LLOQ）浓度，可以降低尿液药物检测项目中滥用药物的假阴性率。
