大规模人群筛检的假阴性分析

False negatives of screening in large-scale population

【目的】探讨传染病在低感染率流行状态下,筛检试验的阴性预测值和假阴性数量在不同人群感染率、灵敏度和特异度情况下的变化趋势。【方法】通过数据模拟,假定人口数为2 000万,分别计算人群疾病感染率为0.1%、1.0%和5.0%的情况下,不同灵敏度(75.0%、80.0%、85.0%、90.0%、95.0%、99.0%)和特异度(90.0%、95.0%、99.0%、99.9%)组合的阴性预测值、真阴性数和假阴性数。【结果】当人群感染率为0.1%时,灵敏度≥75.0%和特异度≥90.0%的筛检试验在2 000万的人群中可发现的真阴性数约为1 798.20万~1 996.00万人。当灵敏度为75.0%时,阴性预测值为99.972%~99.975%,假阴性人数为0.50万人;当灵敏度提高至99.0%时,阴性预测值为99.999%,假阴性人数减少至200人。当人群感染率为1.0%时,灵敏度≥75.0%和特异度≥90.0%的筛检试验在2 000万的人群中可发现的真阴性数约为1 782.00万~1 978.02万人。灵敏度为75.0%时,阴性预测值为99.720%~99.748%,假阴性人数为5.00万人;当灵敏度提高至99.0%时,阴性预测值升高至99.990%,假阴性人数减少至2 000人。当人群感染率为5.0%时,灵敏度≥75.0%和特异度≥90.0%的筛检试验在2 000万的人群中可发现的真阴性数约为1 710.00万~1 898.10万人。当灵敏度为75.0%时,阴性预测值为98.559%~98.700%,假阴性人数可达25.00万人;当灵敏度达到99.0%时,阴性预测值升高至99.942%~99.947%,假阴性人数减少至1.00万人。人群感染率越低,筛检中出现的假阴性者人数越少。【结论】开展大规模筛检中的假阴性者人数随着感染率的升高而成倍的增加,应尽可能在传染病流行的早期开展筛检,以尽快控制疾病的流行。

[Objective]To explore the changing trend of negative predictive value and number of false negatives in screening tests under the condition of low infection rate of infectious diseases.[Methods]Assuming that the population is 20 million,to calculate the negative predictive value,numbers of true negatives and false negatives of the combination of different sensitivity(75.0%,80.0%,85.0%,90.0%,95.0%,99.0%) and specificity(90.0%,95.0%,99.0%,99.9%) when the disease infection rate of the population is 0.10%,1.0% and 5.0%respectively.[Results]When the population infection rate is 0.1%,with the screening test sensitivity ≥75.0% and specificity ≥90.0%,the number of true negatives in 20 million people is about 17.98-19.96 million. When the sensitivity is 75.0%,the negative predictive value is99.972%-99.975%,and the number of false negatives is 5 000;When the sensitivity increases to 99.0%,the negative predictive value is99.999%,and the number of false negatives decreases to 200. When the population infection rate is 1.0%,a screening test with sensitivity ≥75.0% and specificity ≥90.0% can detect about 17.82-19.78 million true negatives in 20 million population. When the sensitivity is 75.0%,the negative predictive value is 99.720%-99.748%,and the number of false negatives is 50 000;When the sensitivity increases to 99.0%,the negative predictive value increases to 99.990%,and the number of false negatives decreases to 2 000. When the population infection rate is5.0%,with sensitivity ≥75.0% and specificity ≥90.0%,the number of true negatives in 20 million people is about 17.10-18.98 million;when the sensitivity is 75.0%,the negative predictive value is 98.559%-98.700%,and the number of false negatives can reach 250 000;When the sensitivity is 99.0%,the negative predictive value increases to 99.942%-99.947%,and the number of false negatives decreases to 10 000. The lower the infection rate of the population,the fewer false negatives will appear in the screening.[Conclusion]The number of false negatives in large-scale screenings increases exponentially with the increase of infection rate. Screenings should be carried out as early as possible in a pandemic of infectious diseases,so as to control the spread of the pandemic as soon as possible.