Relation of predictive value to sensitivity and specificity of a diagnostic test

This paper discusses how the positive and negative predictive values vary withcontrary variations of sensitivity and specificity at a certain disease prevalence.Let thesensitiviy be Se and the specificity be Sp at the initial cutoff point,correspondingly Se’and Sp’ at a new cutoff point:A=Se’/Se:B-(1-Sp’)/(1-Sp):C=Sp’/Sp;D=(I-Se’)/(I-Se).Moving the cutoff point from the initial point to the new point,if the contrary variationsof the sensitivity and specificity satisfy the inequality A】B,then the positive predictivevalue increases,otherwise it decreases or remains unchanged.If the variations satisfy theinequality C】D,then the negative prcdictive value increases,otherwise it decreasses or re-mains unchanged.

Diagnosis of Helicobacter pylori Infection in Low Out-Outcome Country: Rapid Urease Test, Serological Test, versus Direct Microbiological Examination with Gram Stain

Introduction: Helicobacter pylori is a gram-negative bacillus responsible for numerous gastroduodenal pathologies, and this infection is a public health problem. The prevalence of infection with this bacterium remains high in countries with limited resources. Diagnosis relies mainly on numerous invasive and noninvasive methods. The aim of this work was to evaluate the different indirect diagnostic methods using bacterial cultures. Methods: We conducted a cross-sectional and analytical study from January to May 2022 in the gastroenterology departments of Douala General Hospital and Douala Military Hospital. All patients aged 18 years and older who were in the gastroenterology consultation and agreed to participate were included in our study. Sociodemographic, clinical, and paraclinical data were collected. Urease, liquid urea, and culture tests were performed from the specimens obtained by fibroscopy. Serological tests were performed on the blood sample. Results: 101 patients were included, 58 were female and 43 were male, for a sex ratio of 1.3. The mean age was 44.2 ± 16 years. The prevalence of infection was 90.5%, 44.1%, 40.6% and 21.8% for serology, direct microbiological examination, RUT (rapid urea test) and culture, respectively. Comparison of the different tests showed sensitivity and specificity of 67.1% and 64%, respectively, for RUT, 100% and 73.7%, respectively, for direct microbiological examination, and 100% and 14.8%, respectively, for serology. The positive and negative predictive values were 39.5% and 100% for serology, 39% and 85% for RUT, and 55.6% and 100% for direct microbiological examination, respectively. Conclusion: The prevalence of Helicobacter pylori infection depends on the type of test used. Direct examination is more reliable than RUT and serology.

诊断试验灵敏度与特异度似然比预测值的变化关系研究

目的:探索诊断试验的灵敏度与特异度、似然比、预测值的变化关系。方法:应用数学方法证明了确定人群中提高灵敏度(Se)时,特异度(Sp)、阳性似然比(+LR)、阴性似然比(-LR)、阳性预测值(+PV)、阴性预测值(-PV)的数学变化关系,并给出了实例分析。结果:提高灵敏度时,特异度、预测值和似然比的升高或降低,与病人诊断试验阳性数的增量、非病人诊断试验阳性增量等有关。结论:提高灵敏度时,特异度降低或不变,似然比和预测值存在升高、不变或降低等情况;阴性似然比与阴性预测值的变化方向相反。

行列资料诊断试验预告值和准确度的一次性标化研究

本文建立了行列资料诊断试验预告值和准确度的一次性标化方法，省去了标化过程理论样本Ｎｔ的设定和求有关理论值的计算过程，导出行列资料中标准化Ⅰ级阳性预告值和标准化Ⅱ级阳性预告值、标准化Ⅰ级阴性预告值和标准化Ⅱ级阴性预告值、标准化可疑预告值和标准化准确度的一次性标化公式。分析了标化与非标化预告值的关系及转化规律。

磁共振弥散加权成像在口腔鳞癌颈部淋巴结转移中的初步应用

目的:评价磁共振弥散加权成像(MR-DWI)在口腔鳞状细胞癌(OSCC)颈部转移性淋巴结诊断中的应用价值。方法:结合术后病理结果,分别分析51例OSCC患者的CT检查资料及20例OSCC患者的MR-DWI影像资料,采用SPSS16.0软件包中的χ2检验,比较不同检查方法对OSCC颈部转移淋巴结诊断的准确性,确定OSCC患者头颈部MR-DWI扫描的最佳参数设置。结果 :CT、MR-DWI扫描检查淋巴结转移情况与术后病理结果的符合率分别为69.2%和85.0%。MR-DWI取b值为800s/mm2时图像质量最佳,其诊断的敏感度及特异性分别为87.5%和83.3%,CT为76.2%和63.3%。经χ2检查,MR-DWI扫描诊断结果与术后病理诊断结果具有中等相关性,Kappa值=0.694(P<0.005)。结论:OSCC颈部转移淋巴结的MR-DWI影像特征与病理诊断结果具有较好的相关性,且与CT检查相比,MR-DWI能够更准确地预测OSCC颈部淋巴结转移情况。

标准化预告值和准确度与灵敏度特异度的关系分析

本文分析了标准化阳性预告值SPPV、标准化阴性预告值SNPV、标准化准确度SAc和标准化错诊率与灵敏度、特异度的关系,即:①当Se=Sp时,SPPV=SNPV=SAc=Se,SWDR=1-Se;②当Se+Sp=1时,SPPV=SNPV=SAc=SWDR=0.5;③当Se+Sp>1时,Sp的增减对SPPV的影响大于Se,而Se的增减对SNPV的影响大于Sp,当Se|Sp<1时,Sp的增减对SPPV的影响小于Se,而Se的增减对SNPV的影响小于Sp;④SPPV和SNPV随Se和Sp的增大而呈指数增长,SPPV与Se、SNPV与Sp的指数增长曲线增长幅度趋于递减,而SPPV与Sp、SNPV与Se的增长幅度不断递增。Se和Sp对SPPV和SNPV的影响呈对称性;⑤SAc与Se和Sp呈正比,而SWDR与Se和Sp成反比。

四种艾滋病病毒抗体筛查试剂检测性能评价

目的通过对比分析艾滋病病毒（HIV）抗体筛查阳性结果与免疫印迹试验（WB）结果，评价4种HIV抗体筛杏试剂榆测性能。方法2004年1月至2009年6月，分别用中山生物工程有限公司、荷兰生物梅里埃有限公司、珠海丽珠有限公司生产的3种酶联免疫吸附试验（enzyme linked immunosorbentassay，ELISA）试剂初筛血清HIV抗体，用美国雅培Determine HIV-1／2胶体硒标试剂、原试剂复检。筛查阳性样本用WB法进行确认。结果共检测206151例患者血清HIV抗体，确认HIV抗体阳性193例（0．094％）：3种ELISA试剂敏感度、阴性预期值均为100％；雅培试剂分别为93．93％、91．67％，其漏检的样小均为WB不确定：中山、梅里埃、丽珠、雅培试剂的特异度分别为99．88％、99．89％、99．96％、89．38％；阳性预期值（study predictive value of apositive test result，PVP）分别为35．58％、46．46％、76．61％、92．20％；功效分别为99．88％、99．89％、99．96％、91．98％；3种ELISA试剂ROC曲线下面积分别为0．93、0．99、0．95。丽珠的PVP明显高于中山（Х^2=45．804，P=0．000）、梅咀埃（Х^2=25．231，P=0．000）；梅里埃的PVP比中山高，但无统计学意义（Х^2=2．488，P=0．115）；雅培PVP最高（与丽珠相比，Х^2=18．633，P=0．000）。在WB确认阳性、小确定、阴性组，均存在S／CO值[样本（sample）吸光度值／临界值（cutoff）]〈6或≥6的样本。中山试剂确认阳性组S／CO值（14．29±2．63）明显高于阳性-阴性组（2．80±3．25）（t=17．652，P=0．000）。悔里埃试剂确认阳性组S／CO值（16．09±2．35）明显高于阳性-阴性组（2．14±1．91）（t=31．622，P=0．000）：丽珠试剂确认阳性组S／CO值（11．54±1．95）明显高于阳性-不确定组（5．54±3．57）（t=6．386，P=0．000）、阳性-阴性组（3．25±2．41）（t=21．772，P=0．000）；阳性-不确定组S／CO值则高于阳性-阴性组（t=2．301，P=0．033）。结论4种筛查试剂性能良好，根据S／CO值不能准确估计WB确认结果，筛查阳性后必须进行确认。