Spiehler V R, O'Donnell C M, Gokhale D V
Diagnostic Products Corp., Los Angeles, CA.
Clin Chem. 1988 Aug;34(8):1535-9.
Confirmation of presumptive positive urine drug screens, necessary to minimize the reporting of false-positive results, can be costly and time-consuming. The predictive value model can be used to select the confirming tests and to calculate the confidence of the result. The predictive value of a test result is the probability, based on the sensitivity and specificity of the test, that the result is a true positive or a true negative. The predictive value model applied to toxicology screening tests for drugs of abuse showed that prevalence, in addition to sensitivity and specificity, was the factor controlling the confidence level of a result. For example, the predictive value of a positive result for a screening test that has a sensitivity of 99% and a specificity of 99%, applied to screening in a population with a prevalence of 1% is 0.50; for a prevalence of 10%, it is 0.92. Confirmation with a second, chemically independent, test of equal sensitivity and specificity increases the predictive value to 0.99.
为尽量减少假阳性结果的报告，对尿液药物筛查初步阳性结果进行确认可能既费钱又耗时。预测值模型可用于选择确认试验并计算结果的可信度。试验结果的预测值是基于试验的敏感性和特异性，该结果为真阳性或真阴性的概率。应用于药物滥用毒理学筛查试验的预测值模型表明，除敏感性和特异性外，患病率是控制结果置信水平的因素。例如，一项敏感性为99%、特异性为99%的筛查试验，应用于患病率为1%的人群进行筛查时，阳性结果的预测值为0.50；患病率为10%时，预测值为0.92。用第二项敏感性和特异性相同的化学独立试验进行确认，可将预测值提高到0.99。
