Ross University Principles Of Diagnostic Testing PDF

PRINCIPLES OF DIAGNOSTIC TESTING PEDRO BITTENCOURT, DVM, MSC, PHD PRINCIPLES OF INFECTIOUS DISEASES HOW DO WE KNOW WHAT IS GOING ON? DIAGNOSTIC TESTS Learning Objectives Describe the importance of diagnos...

PRINCIPLES OF DIAGNOSTIC TESTING PEDRO BITTENCOURT, DVM, MSC, PHD PRINCIPLES OF INFECTIOUS DISEASES HOW DO WE KNOW WHAT IS GOING ON? DIAGNOSTIC TESTS Learning Objectives Describe the importance of diagnostic tests Understand the basis of diagnostic test and sample selection Understand the indicators of diagnostic test validity Sensitivity, Specificity, Predictive Values Why are diagnostic tests important? Confirm/exclude diagnosis Determine treatment strategies Epidemiological surveillance Prevention, control and eradication strategies Identification of new pathogens Phases of Testing Pre-analytical Test selection; sampling; storage; transportation Analytical Handling and analysis of the specimen Post-analytical Report results; interpretation Test Selection Determined by: Type of pathogen Type sample needed Test characteristics Phase of the disease Availability Cost Considerations About Samples Samples must be correctly: Selected Blood? Tissues? Feces? Urine? Sputum? Collected Timing? Sterile? Multiple? Stored & transported Tubes? Transport medium? Temperature? Determined by the type of test, pathogen, and phase of disease Inadequate samples = Inadequate results Understanding Test Results: The result of a diagnostic test can be divided into 4 categories: Cut-off: value that divides results between positive or negative Understanding Test Results: Diseased Non-diseased Positive test result True Positive (TP) False Positive (FP) Negative test result False Negative (FN) True Negative (TN) Diagnostic Sensitivity & Specificity: How Reliable is a Test? Diagnostic Sensitivity Measures the capacity of a test to correctly identify the positive individuals (True positives). TP Determined by the equation: × 100 TP + FN Diagnostic Specificity Measures the capacity of a test to correctly identify the negative individuals (True negatives) TN Determined by the equation: × 100 TN + FP Diagnostic Sensitivity & Specificity: How Reliable is a Test? Diseased Non-diseased Positive test result True Positive (TP) False Positive (FP) Negative test result False Negative (FN) True Negative (TN) Sensitivity: Specificity: TP TN TP + FN TN + FP  Notice the cut-off change from A to B. What are the impacts of this change? B A  Notice the cut-off change from figure A to B. What are the impacts of this change? A B TP TN SENSITIVITY = × 100 SPECIFICITY = × 100 TP + FN TN + FP  Notice the cut-off change from figure A to B. What are the impacts of this change? A B More FPs Fewer FNs task Confountytrust × 100 Saeng TP TN SENSITIVITY = Sensitivity ↑ SPECIFICITY = × 100 Specificity ↓ TP + FN TN + FP Test Predictive Value In clinical practice, what you need to know: What is the probability that a test-positive animal from the population you are testing is truly diseased? What is the probability that a test-negative animal from the population you are testing is truly healthy? Test Predictive Value Positive Predictive Value Probability of a positive test being a TP totalposition TP Determined by: × 100 TP + FP Negative Predictive Value Probability of a negative test being a TN TN tollgate Determined by: × 100 TN + FN Prevalence has a strong impact on predictive values Prevalence Proportion of a population affected by a disease at a specific time A “photograph” of a specific moment Purlace he Not to be confused with Incidence, which refers to the number os new cases of a disease in a time interval e Predictive Values: How Reliable is a Test Result? Diseased Non-diseased Positive Predictive Value: Positive test result True Positive (TP) False Positive (FP) TP × 100 TP + FP Negative Predictive Value: Negative test result False Negative (FN) True Negative (TN) TN × 100 TN + FN Impact of prevalence in the PPV in tests with different levels of diagnostic sensitivity and specificity adf.tn GEE Impact of prevalence in the NPV in tests with different levels of diagnostic sensitivity and specificity  Diseased Non-diseased Positive Predictive Value: Positive test result True Positive (TP) False Positive (FP) TP × 100 TP + FP Negative Predictive Value: Negative test result False Negative (FN) True Negative (TN) TN × 100 TN + FN Sensitivity: Specificity: Accuracy: TP TN TP + TN × 100 × 100 × 100 TP + FN TN + FP TP + FP + TN + FN Based on the following data, calculate: Sensitivity, Specificity, PPV and NPV. IF Diseased Non-diseased Positive test result Negative test result 0105 25 00 23 847 it 105 130 80.7 Ppv spannan Based on the following data, calculate: Sensitivity, Specificity, PPV and NPV. Diseased Non-diseased Positive test result 78 88 Negative test result 5 829 QUESTIONS? THANK YOU FOR ATTENDING! ©2021 Ross University School of Veterinary Medicine. All rights reserved.