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1、提高诊断性试验效率的办法：联合试验,平行试验：同时做几个试验，只要有一个阳性，即可认为有患病证据。平行试验提高了敏感度和阴性预测值，但降低了特异度及阳性预测值。 如联合用阻抗体积描记图及注射125I纤维蛋白原下肢扫描诊断下肢深静脉栓塞。单独应用这2种方法时，2种方法的敏感度均为74%，平行试验可使敏感度提高到94%。 Sen=Sen1 + Sen2 - Sen1 X Sen2 Spe=Spe1 X Spe2 验后比=验前比 X LR1 X LR2,联合试验,序列试验：依次相继的试验，要所有的试验阳性才能做出诊断。序列试验提高了特异度及阳性预测值。但降低了敏感度及阴性预测值。 例如：诊断心肌梗死
2、的CPK、AST、LDH，没有一种试验是很特异的，如采用序列试验，即三项均阳性才能诊断，这样可提高诊断心肌梗死的特异度。 SEN = SEN1 X SEN2 SPE = SPE1 +SPE2 - SPE1 X SPE2,ROC曲线,ROC曲线,用不同的临界点分别计算敏感度、特异度，再用敏感度及假阳性率(1-Spe)做图。如分别以CPK 280、80、40、1为临界点，计算SEN、SPE 280 80 40 1 敏感度 42% 93% 99% 100% 特异度 99% 88% 68% 0%,ROC曲线,诊断性试验的应用,根据临床问题找出最恰当的研究文章 评价文章的科学性 试验是否与金标准进行盲法
3、比较 是否每个被测者都做了参照试验进行评价 所研究的样本是否包括临床工作中将使用该诊断试验的各种病人 对诊断性试验的实施方法描述是否详细，足以让读者重复,诊断性试验的应用,估计临床应用的重要性 估计疾病的验前概率 说明和应用关于敏感度和特异度的资料 应用似然比 将临床研究结果应用于自己的病人 结果是否适用并能提供给我的病人 诊断性试验是否改变了对患病概率的估计 诊断性试验是否改变了对病人的处理 病人能否从诊断性试验获益,验前概率的估计,诊断性试验中验前概率的判断：根据个人经验，人群患病率资料，实践资料，文献描述，对不同情况下验前概率的研究资料。,一些验前概率的例子,临床症状和问题 资料来源 检
4、查内容 疾病概率 慢性病贫血 北美乡村医院病房 临床检查 感染36% 90例成人 血液检查 炎症6% 其他选择性试验 恶性肿瘤19% 肾病15% 其他24% 眩晕2周 北美某一城市初级 临床检查、神经科 眩晕病54% 保健单位100例 眼科、心理测试、 精神性16% 成年病人 其他选择性试验 多源性13% 其他19% 原因不明8%,验前概率举例,临床疾病或问题 资料来源 检查内容 疾病概率 原因不明呼吸困难 北美肺科门诊72例 标准的检查 呼吸道疾病36% 4周 成年病人 试验及治疗 心源性14% (体检、胸片、肺 通气过度19% 功能测定不能解释） 其他12% 不能解释19% 心悸 北美一城
5、市急性病 临床检查：心脏 心源性43% 中心190例病人 心理测试、其他 精神性31% 选择性试验 混杂性10% 原因不明16%,诊断性试验的价值在于明确临床诊断、确定相应治疗措施并改变病人的结局,诊断性试验的应用,诊断性试验可用于： 诊断疾病 筛查无症状的病人 疾病的随访 判断病情的严重性 估计疾病的临床过程及预后 估计对治疗的反应 测定目前对治疗的反应,诊断性试验的应用,Clinical scenario You admit a 77 year old female with community acquired pneumonia to the ICU. She was admitted
6、 from the emergency department with hypoxemia that is refractory to supplemental oxygen. She is intubated but this required fiber optic intubation because she could not be intubated by direct laryngoscopy. She was placed on antibiotics. She does not have other significant past medical history. Two d
7、ays later, her fraction of inspired oxygen is 40% and she is off positive end expiratory pressure. You decide she is ready to be extubated but the critical care fellow expresses concern that she will fail extubation and will not be able to be reintubated. You state that you would like to use some di
8、agnostic test to help predict if she will be successfully extubated. Your fellow states that the respiratory rate to tidal volume ratio can be used to predict successful extubation and her ratio is 50.,提出临床问题，并进行检索 You from the question: In mechanically ventilated patients, can the respiratory rate
9、to tidal volume ratio be used to predict successful extubation? You perform a MEDLINE search using the Mesh terms extubation and sensitivity and specificity and find an article about predictors of successful extubation (NEJM 1991:324:1445-1450）,按照诊断性试验的评价标准进行评价 Are the results of this diagnostic tes
10、t valid? 1. Was there an independent, blind comparison with a reference (“gold“) standard of diagnosis? Yes. 2. Was the diagnostic test evaluated in an appropriate spectrum of patients (like those in whom it would be used in practice)? Yes. 3. Was the reference standard applied regardless of the dia
11、gnostic test result? Yes.,Are the valid results of this diagnostic study important?,Sensitivity = a/(a+c)= 29/36= 80% Specificity = d/(b+d) = 25/28= 89% +LR = sens/(1-spec)= 7.5 - LR = (1-sens)/spec = 0.22 +PV = a/(a+b)= 91% - PV = d/(c+d)= 79% Pre-test Probability (prevalence) = (a+c)/(a+b+c+d) = 5
12、6% Pre-test odds = prevalence/(1-prevalence) = 1.28 Post-test odds = Pre-test odds x LR = 7.5 x 1.28=9.6 Post-test Probability = post-test odds/(Post-test odds + 1) = 9.6/10.6= 91%,Is the diagnostic test available, affordable, accurate, and precise in your setting? Can you generate a clinically sens
13、ible estimate of your patients pre-test probability (from practice data, from personal experience, from the report itself, or from clinical speculation),Yes, the authors gave a detailed description of how the test was performed Approximately 70%,Will the resulting post-test probabilities affect your
14、 management and help your patient? (Could it move you across a test-treatment threshold?; Would your patient be a willing partner in carrying it out?) Would the consequences of the test help your patient?,Her respiratory rate to tidal volume ratio of 50 gives her a post-test probability of 95% and t
15、his crosses my treatment threshold of 90% Yes, since she is a difficult intubation, we want to minimize our chance of a false positive (we state she could be successfully extubated but she fails).,诊断性试验评价,题目：心电图活动平板运动试验与冠状 动脉造影结果对照分析 作者：黄丽敏 李榕生 来源：中华心律失常学杂志 2001；5 （3）：164-166,内容摘要：作者以冠状动脉造影为标准诊断冠心病，
16、并对101例患者进行了心电图活动平板运动试验，以评价运动试验对冠心病的诊断价值。发现运动试验诊断冠心病的敏感性（敏感度）为85.29%，特异度为82.09%，表明心电图活动平板运动试验是目前诊断冠心病较理想的非创伤性检查方法。,诊断标准：冠脉造影发现冠状动脉管径狭窄50% 检测对象：进行活动平板试验的患者1840例，其中做冠脉造影者101例 方法：MECACART大型平板运动心功能检测系统，Bruce方案 运动前及运动停止后每隔12分钟记录12导联心电图，直至6分钟终止或延迟至ST段开始恢复。 阳性判断标准：运动中或运动后心电图出现J点后60ms ST段水平或下斜型下移=0.1mV或呈损伤型抬
17、高0.2mV或运动诱发典型心绞痛(由心血管专科医师判断)。,结果： 冠心病组 非冠心病组 运动试验 29(真阳性) 12(假阳性) 阳性 运动试验 5（假阴性） 55（真阴性） 阴性 34 67,敏感度：a/a+c=29/34=85.29% 特异度：d/b+d=55/67=82.09% +LR=0.8529/(1-0.8209)=4.76 -LR=(1-0.8529)/0.8209=0.1792 ACC=(29+55)/101=83.17 Prev=34/101=33.7% +PV=a/（a+b）=29/（29+12）=70.73% -PV=d/(c+d)=55/(5+55)=91.67%,评
18、价： 是否采用盲法将诊断性试验与标准诊断作过对比研究？ 不详。作者采用了目前国际上通用的“金标准”冠脉造影术，而且将运动心电图试验结果与金标准进行了对比。未提及是否用盲法。 除强调盲法外，每个受检者都应经过金标准试验检查。假如作者只将运动试验阳性者做冠脉造影，考虑到冠脉造影的创伤性及患者的依从性，运动试验阴性者只抽出一部分（比如1/10）做冠脉造影。事实上，有些运动试验阴性者也可能是冠心病患者，这样的研究结果就可能夸大运动试验的敏感性，造成偏倚。,例如，对儿童语言发育延缓的筛选项目评价中，研究者从许多不同人群中随机抽样选出50例儿童对其语言能力进行筛检，并进行评价。金标准是一个结构严谨的问卷调
19、查，50例筛选阳性的儿童用此问卷调查，另外，在500例筛检阴性者中，再抽出50例儿童使用标准问卷调查，结果如下：,金标准 + - 合计 筛查 + 35 15 50 试验 - 4 46 50 39 61 100 结果：敏感度=90% 特异度=75% 故作者认为，此筛检方法敏感度高，可以作为筛检试验的方法。,但是，实际情况如下： 金标准 + - 合计 筛查 + 35 15 50 试验 - 40 460 500 76 475 550 真正的结果： 敏感度=46% 特异度=96.8%,两者敏感度不同,说明存在工作偏倚。工作偏倚可用下列方法加以纠正： 有误差的敏感度= a/（a+c） 纠正的敏感度=（a
20、/f）/（a/f + c/g） 有误差的特异度= d/（b+d） 纠正的特异度=（d/g）/（d/ g + b/f） f = 试验阳性者再做金标准试验的比例 g = 试验阴性者再做金标准试验的比例,被检查的病例是否包括各型病例及个别易混淆的病例？ 不详。作者未提到如何纳入病人，也未提到病人为什么做运动心电图或冠脉造影。 病例的来源和实验安排是否做了叙述？ 没有 诊断性试验的重复性如何？ 未报道重复性试验结果,试验中所确定的正常值是否可靠？ 较可靠，从试验结果的假阳性及假阴性率来看，正常值较可靠 在一系列试验中，该试验是不是最正确的？ 不是 试验步骤叙述是否明确，能否进行重复试验？ 试验步骤叙述
21、清楚，应该能进行重复试验 该试验的实用性如何？ 难以评价，可能有一定的实用性。作者应重新设计，以得出可靠结论。,Biliary scintiscan had high sensitivity and specificity for predicting pathologic findings in the common bile duct,Mathur SK et al Br J Surg. 2000 Feb;87:181-5,Question In patients with symptomatic gallstone disease, can biliary scintiscan pred
22、ict the presence of pathologic findings in the common bile duct (CBD)?,Design A blinded comparison of scintiscan and ultrasonography alone or combined with clinical or standard criteria (history of jaundice or acute pancreatitis, elevated serum bilirubin and alkaline phosphatase levels, and visualiz
23、ation of a stone or presence of dilated bile ducts on ultrasonography) and modified criteria (jaundice within the past 3 mo, elevated serum bilirubin and alkaline phosphatase levels, and visualization of a stone or presence of dilated bile ducts on ultrasonography).,Setting A tertiary referral cente
24、r in Bombay, India. Patients 75 consecutive patients (mean age 46 y, 61% women) with symptomatic gallstone disease. Patients with acute cholecystitis, acute pancreatitis, or cholangitis were excluded.,Description of tests and diagnostic standard Biliary scintigraphy was done using intravenous inject
25、ion of 5 Ci 99mTc-radio-labeled mebrofenin with a recording at baseline and at 1 and 2 hours. Reading of recordings was blinded using predetermined criteria (standard and modified) for pathologic findings in the CBD.,Positive ultrasonographic criteria were visualization of a CBD stone, presence of i
26、ntrahepatic bile duct dilatation, or common hepatic duct or CBD size 7 mm. The diagnostic standard was endoscopic or preoperative cholangiography; if calculi were found, endoscopic sphincterotomy or open surgical exploration of the CBD was done.,Main outcome measures Sensitivity and specificity of f
27、eatures of biliary scintiscan, ultrasonography, and clinical criteria for predicting pathologic findings in the CBD.,Main results Sensitivity and specificity for biliary scintiscan alone and combined with ultrasonography were high (Table). The sensitivity and specificity of other features or parameters are listed in the table.,Conclusion Sensitivity and specificity for biliary scintiscan alone and combined with ultrasonography were high.,