诊断试验评价案例讨论

诊断试验评价案例讨论 严卫丽教授博士新医大公共卫生学院流行病学与卫生统计学教研室电话：4366351 Email：01.weili@gmail.com

Screening test outcomes: For dichotomous - positive or negative For continuous - categorize to positive or negative If screening test finding is: Positive Negative right: true positive wrong: false positive right: true negative wrong: false negative

Population reality Disease No disease Test results Positive Negative False Positive True Positive False Negative True Negative TP ability to identify TP + FN those with disease TN ability to identify TN + FP those w/o disease Sensitivity= Specificity=

True characteristics in the population Disease No disease 80 100 800 900 Sensitivity = = 80% Specificity = = 89% Results of screening Positive Negative Total 80 100 180 820 20 800 100 900 1000 Example: Pop: 1000 w/dis: 100 w/o dis: 900

Result of a Dichotomous Test with Disease Status Population Test Results Positive Negative With Disease W/O Disease

Predictive Value of a Test • If the test results are positive in this patient, what is the probability that this patient has the disease? • What proportion of patients who test positive actually have the disease in question?

Positive Predictive Value of a Test: PPV = Negative Predictive value: With negative result, what is the probability that the patient does not have the disease? NPV = True positive Total positive True Negative Total negative

Relationship betweenPredictive Value and Prevalence Predictive value improves as prevalence increases. Relationship between Predictive Value and Specificity Predictive value improves as specificity of a screening test increases.

Continuous Variables: Cutoff • Defining level of risk factor for intervention: lipids, blood pressure, glucose, CRP, etc • What level cutoff for medical intervention? cholesterol: from LRC to HPS • What test? cholesterol: LDL, HDL, ratio, nonHDL-C, triglycerides & glucose: fasting or postprandial

Is LDL/HDL ratio better than LDL? • Better for what?

Is OGTT better than FPG? • Better for what?

Screening for Type 2 Diabetes: Strong Heart Study Wang, Diabetes Care, 2002.

ROC analyses of waist circumference, Waist-to-hip ratio, and WHTR to Obesity defined by BMI(boys) WC WHR WHtR

Area under the curve of Waist, WHR and WHTR (WI) WHtR

Optimal thresholds of WHTR for defining overweight and obesity and corresponding sensitivity and specificity in Chinese boys and girls aged 8-18 years

Correlation between WHTR and BMI with age Boys: r= -0.108, p<0.001 Girls: r= 0.035, p<0.001 WHTR Boys: r= 0.413, p<0.01 Girls: r= 0.39, p<0.001 BMI, kg/m2 Age, yrs Girl Boys

例1 某社区的人口为5万人，现拟用血糖试验来筛检糖尿病。不同的筛检标准及其准确性见下表：问题1. 按下面的情况，分别列出四格表，通过计算填入相应的数字，并计算预测值。

表4-2. 血糖试验不同筛检标准的准确性 • 社区患病率为1.0%，筛检标准为≥130 mg/dl • 社区患病率为1.0%，筛检标准为≥180 mg/dl • 社区患病率为2.0%，筛检标准为≥180 mg/dl

例2 通过检测血清中的甲胎蛋白（AFP)、铁蛋白（SF）或者谷氨酰转移酶 II(GGT-II),可以用来诊断肝癌。下表列出了这3种方法的准确性。

问题 • 如果要在人群中筛检肝癌，用这3种方法中的哪种收益会最大？ • 如果某社区有50万人口，肝癌的患病率为20/10万，在该社区中用GGT-II来筛检肝癌是，会造成多少假阳性？阳性预测值是多少？它表示什么？ • 通过该案例，你得到什么启发？

联合试验 • 并联两项试验，任何一项阳性就算阳性 • 串联两项试验，同时阳性时才算阳性

例3. 联合试验 下表为尿碘和血碘对某镇居民筛检，检查甲状腺功能异常的结果。

问题 • 请分别计算单纯的血碘试验、尿碘试验的灵敏度、特异度，以及并联试验和串联试验的灵敏度和特异度 • 同单纯某一项筛检试验相比，联合试验的灵敏度和特异度有何改变？ • 如果让你主持一项较大规模的甲状腺功能异常的普查工作，你认为是采用单一某一项试验还是联合试验中某一组合？为什么？

Thank you !

诊断试验评价 案例讨论