Diagnostic Tests Afshin Ostovar Bushehr University of Medical Sciences Bushehr, /7/20151

A normal individual is a person; Who has not been sufficiently examined 12/7/20152

Introduction It is necessary to distinguish between people in the population who have the disease and those who do not. clinical arena Public health arena How good is the test in separating populations of people with and without the disease in question? 12/7/20153

Biologic Variation of Human Populations 12/7/20154 Bimodal curve

12/7/20155 Unimodal curve

Validity of screening Tests Sensitivity: o the ability of the test to identify correctly those who have the disease. Specificity: o the ability of the test to identify correctly those who do not have the disease. 12/7/20156

Tests with Dichotomous Results 12/7/20157 Gold Standard

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False Positive effects Burden on the health care system Labeling effect 12/7/20159

False Negative effects Deprivation from effective treatment It depends on: the nature and severity of the disease the effectiveness of available intervention measure Whether the effectiveness is greater if the intervention is administered early in the natural history of the disease 12/7/201510

Tests of Continuous Variables 12/7/ Sensitivity= 5/20 = 25% Specificity= 18/20 = 90%

Tests of Continuous Variables 12/7/ Sensitivity= 17/20 = 85% Specificity= 6/20 = 30%

Different cut-offs 12/7/201513

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Multiple Tests Sequential (Two-stage) Testing Simultaneous (Parallel) Testing 12/7/201519

Sequential (Two-stage) Testing 12/7/201520

Test 1 Diabetes + _ Test Results + _ /7/201521

Prevalence = 5% Diabetes + _ Test Results + _ /7/201522

Sensitivity = 70% Diabetes + _ Test Results +350 _ /7/201523

Specificity = 80% Diabetes + _ Test Results _ /7/201524

Final Result of Test 1 Diabetes + _ Test Results _ /7/201525

Test 2 Diabetes + _ Test Results + _ /7/201526

Sensitivity= 90% Diabetes + _ Test Results +315 _ /7/201527

Specificity=90% Diabetes + _ Test Results _ /7/201528

Final Result of two Tests Diabetes + _ Test Results _ /7/ Net sensitivity = 315/500 = 63% Net Specificity = 9310/9600 = 98%

Simultaneous Testing 12/7/201530

Test A 12/7/201531

Test B 12/7/201532

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Test A 12/7/201535

Test B 12/7/201536

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Predictive Value Predictive Value Positive If the test results are positive in this patient, what is the probability that this patient has the disease. Predictive Value Negative If the test results are negative in this patient, what is the probability that this patient do not have the disease 12/7/201539

Predictive Value Positive 12/7/201540

The predictive value is affected by two factors: o the prevalence of the disease in the population tested o the specificity of the test being used, when the disease is infrequent. 12/7/201541

Relationship between Predictive Value and Disease Prevalence 12/7/201542

Relationship between Predictive Value and Disease Prevalence 12/7/201543

Relationship between Predictive Value and Disease Prevalence 12/7/201544

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Relationship between Predictive Value and Specificity 12/7/201547

Relationship between Predictive Value and Specificity 12/7/201548

Relationship between Predictive Value and Specificity 12/7/201549

Relationship between Predictive Value and Specificity 12/7/201550