Transcribed Image Text from this Question
SCREENING Learning objectives: At the end of the activity, students are expected to: 1. Define and explain what is screening. 2. Correctly identify and explain the objectives, uses and types of screening tests. 3. Differentiate screening tests and diagnostic tests. 4. Discuss the criteria for successful screening tests. 5. Differentiate sensitivity, specificity, net specificity and net sensitivity. 6. Correlate the computed sensitivity, net sensitivity, specificity and net specificity to screening tests. Pre-Laboratory Discussion: Screening is the presumptive identification of those who probably have disease from those who do not have by means of rapidly applied test in apparently healthy individuals. (WHO). It can be used for the early detection of disease, precursors of disease and susceptibility to disease in individual who do not show any signs of the disease. Preclinical Phase Clinical Phase ‘Outcomes’ (cured; living with the disease; deteriorated; died) Exposure Biological to onset of pathogen disease Symptoms Therapy appear begun Diagnosis Screening (possible relapse & change in therapy) Difference between Screening and Diagnostic Tests Screening Asymptomatic Large group Less accurate Not conclusive Less expensive Not basis for treatment Diagnostic Suggestive clinical picture Single subject Accurate Conclusive Expensive Basis for treatment Criteria for a successful screening test: SUCCESSFUL SCREENING Disease Criteria Test Criteria Criteria for the Disease: Present in population screened • High burden and of high public health concern • Screening and intervention must improve outcome Known natural history of the disease Criteria for the Test: • Reliable, Valid and very safe • Simple and Inexpensive • Acceptable to subjects and providers • Cost effective • Exit strategy VALIDITY is the ability of the test to distinguish between who has the diseases and who does not. With the disease TOTAL а Tested (+) Tested (-) TOTAL Without the disease b d a+d с a+b c+d a+b+c+d a+c Sensitivity is the ability of the test to truly identify those who have the disease. a/(a +c) • Specificity is the ability of the test to correctly identify those who do not have the disease d/(b + d) • Predictive value o Positive Predictive Value is the proportion of individuals with positive test (with the disease). PPV=a/(a+b) Negative Predictive Value is the proportion of individuals with negative test (without the disease) NPV=d/(c + d) • Yield is the amount of previously unrecognized disease that is diagnosed and brought to treatment as a result of screening. Influenced by: Sensitivity of the test o Prevalence of the unrecognized disease o Testing format o Frequency of screening o Extent of participation in the screening program Teaching and Learning Activities: : • Discuss the relationship of sensitivity and specificity. • Identify the possible effects of a false negative and false positive results. Explain the significance of screening in public health • Compute and interpret the predictive value References: 1. Centers for Disease Control and Prevention. Principles of Epidemiology in Public Health Practice, 3rd ed. An Introduction to Applied Epidemiology and Biostatistics, 2011. 2. TOM. 1990. Medicare: A Strategy for Quality Assurance. Voll. K. N. Lohr, ed. Washington, D.C: National Academy Press. 3. Sharma, Manoj et.al. Introduction to Community and Public Health. One Montgomery Street, Suite 1200, San Francisco, CA. John Wiley & Sons, Inc. 2014. ACTIVITY 06: Laboratory report SCREENING Name: Score: Section: Group: Date: PART I. Explain the relationship of sensitivity and specificity as shown in the diagram. Sensitivity Specificity False positive 1. Specificity Sensitivity False negative . 2. 3. Which is better? A test with high sensitivity or a test with high specificity? 4. How will you explain this graph? Criterion value Without disease With disease TN ТР FN FP Test result 5. Enumerate the possible effects of the false negative and false positive results. 6. What is the importance of understanding screening in public health? Part II. A series of tests were conducted among 400 persons with suspected colon cancer. Two hundred fifty (250) patients actually found to have a problem. The results of the examinations were as follows: Colon Cancer Results Present Absent Positive 200 20 Negative 50 130 Total 250 150 Table 1. Results of Fecal Occult Blood Test (FOBT) Colon Cancer Results Present Absent Positive 220 40 Negative 30 110 Total 250 150 Table 2. Results of CEA Compute for the following. (Use the back portion of the lab sheets or a separate paper to show your computations) 1. Sensitivity and Specificity of the: 1.1. Fecal Occult Blood Test (FOBT) 1.2. CEA 2. Assume that the two tests were used simultaneously, 2.1. How many will test positive on FOBT only? 2.2. How many will test positive on CEA only? 2.3. How many will test positive on both tests? 2.4. What is the net specificity of the two tests? Part III. Effects of Predictive value. Table 1. Disease with a prevalence of 10% DISEASE TEST Yes No Positive 80 90 Negative 20 810 100 900 1000 Table 2. Disease with a prevalence of 50% DISEASE TEST Yes No Positive 400 50 Negative 100 450 500 500 450 550 1000 1. Compute positive and negative predictive vales based on the tables shown above. (You may use a separate paper for the computation) 2. Discuss the effects of prevalence on both positive and negative predictive values. Justify your answer based on your computation.
(Visited 1 times, 1 visits today)
