Beyond one-cutoff-fits-all: determining cutoff values for the PTSD checklist for DSM-5 (PCL-5)

<b>Background:</b> There is no universally optimal cutoff score for identifying probable PTSD, which makes reliable PTSD diagnosis challenging not only across different populations but also in different settings. Reliable outcomes require tailoring cutoff scores to the population, intended use (clinical, research, or prevalence estimation), and appropriate statistical methods to ensure their validity. <b>Objective:</b> While previously little emphasis has been placed on thorough methodological evaluation and purpose-driven cutoff selection, this work addresses these gaps by evaluating optimal PCL-5 cutoff scores for clinical use, prevalence estimation, and research in a German-speaking clinical sample. <b>Methods:</b> Previously published data from 443 trauma-exposed individuals in Germany were re-analyzed for this purpose. PTSD was assessed using the PCL-5 and with CAPS-5 clinical interview. Optimal cutoffs were identified using ROC analysis, applying standard estimation methods and prioritising diagnostic utility based on specific objectives. <b>Results:</b> After evaluating various cutoff points for different purposes, we identified the following as most suitable for this sample: a cutoff of 34 for clinical use (sensitivity: 0.892, specificity: 0.645, PPV: 0.824, NPV: 0.763); 38 for prevalence estimation (sensitivity: 0.840, specificity: 0.703, PPV: 0.840, NPV: 0.703); and 42 or 43 for identifying clear-cut cases in research or resource-limited settings (sensitivity: 0.774–0.760, specificity: 0.742–0.761, PPV: 0.848–0.855, NPV: 0.639–0.631). The originally intended cutoffs of 31–33 yielded acceptable to excellent diagnostic utility parameters but were not identified as optimal for any specific purpose. <b>Conclusion:</b> This study highlights the variability in optimal PCL-5 cutoffs, linking selection to specific clinical or research aims. It provides validated cutoffs for PTSD prevalence in a German clinical sample, with limitations regarding generalizability to lower-prevalence populations. Future research should refine cutoffs for diverse populations and improve diagnostic precision. Context matters: PTSD screening requires purpose-specific cutoff scores rather than a universal threshold.Validated cutoffs: this study determines optimal PCL-5 scores for clinical screening, prevalence estimation, and research.Methodological refinement: this study applies a purpose-driven approach to determining PTSD cutoff scores, emphasising statistical rigour and diagnostic utility. Context matters: PTSD screening requires purpose-specific cutoff scores rather than a universal threshold. Validated cutoffs: this study determines optimal PCL-5 scores for clinical screening, prevalence estimation, and research. Methodological refinement: this study applies a purpose-driven approach to determining PTSD cutoff scores, emphasising statistical rigour and diagnostic utility.

**背景：** 目前尚无用于识别疑似创伤后应激障碍（Post-Traumatic Stress Disorder, PTSD）的通用最优截断值，这使得跨人群、多场景下的PTSD可靠诊断颇具挑战。可靠的诊断结果需要针对目标人群、预期用途（临床、研究或患病率估算）定制截断值，并采用合适的统计方法以确保其有效性。
**目标：** 过往研究对方法学的全面评估与基于用途的截断值选择重视不足，本研究针对德语区临床样本，通过评估适用于临床应用、患病率估算及研究场景的最优PCL-5（创伤后应激障碍检查表5）截断值，填补这一研究空白。
**方法：** 本研究重新分析了既往发表的德国443名创伤暴露个体的数据。采用PCL-5与CAPS-5（临床创伤后应激障碍量表5）临床访谈对PTSD进行评估。通过受试者工作特征曲线（Receiver Operating Characteristic, ROC）分析确定最优截断值，采用标准估计方法，并根据特定研究目标优先考量诊断效用。
**结果：** 针对不同用途评估各类截断值后，本研究确定本样本中最适配的截断值如下：临床应用采用34分（灵敏度：0.892，特异度：0.645，阳性预测值（Positive Predictive Value, PPV）：0.824，阴性预测值（Negative Predictive Value, NPV）：0.763）；患病率估算采用38分（灵敏度：0.840，特异度：0.703，PPV：0.840，NPV：0.703）；在研究或资源受限场景中识别明确病例则采用42分或43分（灵敏度：0.774~0.760，特异度：0.742~0.761，PPV：0.848~0.855，NPV：0.639~0.631）。最初推荐的31~33分截断值虽具备可接受至优秀的诊断效用参数，但未被认定为任一特定用途的最优截断值。
**结论：** 本研究揭示了最优PCL-5截断值的变异性，将截断值选择与特定临床或研究目标相绑定。本研究为德语区临床样本中的PTSD患病率估算提供了经过验证的截断值，但其推广至低患病率人群时存在局限性。未来研究应针对多样化人群优化截断值，并提升诊断精准度。
**要点总结：**
场景至关重要：PTSD筛查需采用针对特定用途的截断值，而非通用阈值。
经过验证的截断值：本研究确定了适用于临床筛查、患病率估算及研究场景的最优PCL-5评分。
方法学优化：本研究采用基于用途的方法确定PTSD截断值，强调统计严谨性与诊断效用。