Christchurch Kidney Research Group, Department of Medicine, University of Otago, Christchurch, New Zealand.
Clin J Am Soc Nephrol. 2012 Aug;7(8):1355-64. doi: 10.2215/CJN.09590911. Epub 2012 Jun 7.
New tests should improve the diagnostic performance of available tests. The area under the receiver operator characteristic curve has been the "metric of choice" to quantify new biomarker performance. Two new metrics, the integrated discrimination improvement (IDI) and net reclassification improvement (NRI), have been rapidly adopted to quantify the added value of a biomarker to an existing test. These metrics require the development of risk prediction models that calculate the probability of an event for each individual. This study demonstrates the application of these metrics in 528 critically ill patients with risk models of AKI, sepsis, and 30-day mortality to which the biomarker urinary cystatin C was added. Analogous to the receiver operator characteristic curve, we present a new risk assessment plot for visualizing these metrics. The results showed that the NRI was sensitive to the choice of risk threshold. The risk assessment plot identified that the addition of urinary cystatin C to the model decreased the calculated risk for some who did not have sepsis but increased it for others. The category-free NRI for each outcome indicated that most of those without the event had reduced calculated risk. This was driven by very small changes in calculated risk in the AKI and death models. The IDI reflected those small changes. Of the new metrics, the IDI, reported separately for those with and without the events, best represents the value of a new test. The risk assessment plot identified differences in the models not apparent in any of the metrics.
新的检测方法应该可以提高现有检测方法的诊断性能。受试者工作特征曲线下面积（AUC）一直是量化新生物标志物性能的“首选指标”。两个新的指标，即综合判别改善（IDI）和净重新分类改善（NRI），已经被迅速采用来量化生物标志物对现有检测方法的附加值。这些指标需要开发计算每个个体发生事件概率的风险预测模型。本研究通过对 AKI、脓毒症和 30 天死亡率的风险模型中添加生物标志物尿胱抑素 C 的 528 例危重症患者，演示了这些指标的应用。类似于受试者工作特征曲线，我们提出了一种新的风险评估图来可视化这些指标。结果表明，NRI 对风险阈值的选择很敏感。风险评估图表明，将尿胱抑素 C 添加到模型中会降低一些没有脓毒症的患者的计算风险，但会增加其他患者的计算风险。每个结局的无类别 NRI 表明，大多数没有发生事件的人计算风险降低。这是由于 AKI 和死亡模型中计算风险的微小变化所致。IDI 反映了这些微小的变化。在这些新指标中，IDI 分别报告了有和无事件的情况，最能代表新检测方法的价值。风险评估图确定了模型中的差异，而这些差异在任何指标中都不明显。
