Introduction of Screening for Nursing Students

Epidemiology Unit-10 Lecture

1. Unit-VI Screening Muhammad Shahid MSN,CHQP, BSN, DCN, RN, BSc Ph D Scholar (Ziauddin University) Assistant Professor/Principal School of Nursing Kharadar General Hospital Date:13-02-2024

2.  At the end of this unit, all the students will be able to: Explain the concept of screening. Differentiation between Screening and Diagnostic test Understand the importance of screening. Understand the types of screening. Criteria for successful screening program 2

3.  The early detection of:  Disease  Precursors of Disease  Susceptibility to Disease In individuals who do not show any signs of disease. The presumptive identification of those who probably have disease from those who do not have by means of rapidly applied tests in apparently healthy individuals. 3

4. Clinical disease Hidden burden of disease Iceberg phenomenon gives an idea of progress of a d i s e a s e f r o m i t s s ub c l i n i c a l stages to overt disease HIDDEN: Subclinical cases, carriers, undiagnosed cases.

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6. Screening 6

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8. 8 Screening test 1. Done on apparently healthy individuals Applied to groups Results are arbitrary and final Based on one criteria and cut-off Less accurate Less expensive Not a basis for treatment Initiative comes from investigator Diagnostic test Done on sick or ill individuals Applied on single patient Diagnosis is not final Based on evaluation of a no. of signs/symptoms & lab findings More accurate More expensive Used as a basis for treatment Initiative comes from a patient patient SCREEN I N G TE S T vs . D I AGNOST I C TES T

9. Case Detection Perspective Screening Case / Disease Control Prospective Screening Research Natural History of Disease Health Education Public Awareness 9

10. Reducing disease burden. Classifying people to likelihood of having a particular disease. Mean of identifying high risk groups who warrant further evaluation. 10

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12. It is the best way to find the medical conditions or diseases at an early stage when their treatment is feasible, easy and less expensive. Screening can find or even prevent about half of the new cancer or other cases. Screening tests reveal the risk factor which is a health condition or a behavior that puts us at risk of developing the disease. If we know our risk factors then we can make certain lifestyle changes that ultimately prevent the disease or disorder that they may lead to. For example, high blood pressure, high cholesterol and obesity are the risk factors that may lead to certain diseases such as diabetes, heart diseases or cancer. Provide a track record of your medical information which can be helpful for the doctor. 12

13. Types Of Screening Test Mass High Risk Multiphasic 13

14. Mass screening: Mass screening means, the screening of a whole population or a subgroup. It is offered to all, irrespective of the risk status of the individual. High risk or selective screening: High risk screening is conducted among risk populations only. Multiphasic screening: It is the application of two or more screening tests to a large population at one time instead of carrying out separate screening tests for single diseases 14

15. Before initiating a Screening Programme, a decision must be made whether it abides to all the ethical, scientific and financial justification.  The principles that should govern the introduction of screening programmes were first enunciated by Wilson and Junger(1968) 15

16.  The principles are still broadly applicable today: The condition should be an important health problem. There should be a treatment for the condition. Facilities for diagnosis and treatment should be available. There should be a latent stage of the disease. There should be a test or examination for the condition. 16

17. The test should be acceptable to the population. The natural history of the disease should be adequately understood. There should be an agreed policy on whom to treat. The total cost of finding a case should be economically balanced in relation to medical expenditure as a whole. Case-finding should be a continuous process, not just a "once and for all" project. 17

18.  In 2008, with emergence of new genomic technologies, the WHO synthesized and modified these with the new understanding as follows: Should respond to a recognized need. Defined objectives screening Defined target population. Scientific evidence of screening programme effectiveness. The programme should integrate education, testing, clinical services and programme management. Quality assurance Ensure informed choice, confidentiality and respect Promote equity and access to screening for the entire target population. Programme evaluation should be planned Benefits of screening more than harm 18

19. Successful Screening Criteria for Disease Criteria for Test 19

20. Criteria for Disease: Present in population screened. High burden & of high public health concern. Screening + Intervention must improve outcome. Known natural history of the disease. 20

21. Criteria for Test: Simple and inexpensive Reliable Acceptable Valid Very safe Cost-effective 21

22. The test should be simple to perform, easy to interpret and, where possible, capable of use by paramedics and other personnel. . Ex: Blood and urine tests and ECG for early detection of hypertension

23. 2. RELIABILTY: What Is The Definition Of Reliability ? What Are The Causes Of Unreliability ? 23 Repeatability, Reducibility, Precision. Getting the same results, when the test repeated in same target individuals in the same settings. Observer variation. Subject variation – Biological. Technical method error variation

24. ACCEPTABILITY: The test should not be: Painful. Unsafe. Discomforting /Embarrassing. Socially/ believes not accepted 24

25. 4. VALIDITY:  Ab i l i t y o f t he t e st t o dis t i n guish b e tw e e n w ho h a s the diseases and who does not. Accurately identify diseased and non-disease individuals. An ideal screening test is exquisitely sensitive (high probability of detecting disease) and extremely specific (high probability that those without the disease will screen negative). 25

26. Sensitivity Specificity Pre d i ctive Value Yield 26

27. Ability of the test to truly identify those who have the disease Se n s it i v it y= a/(a+c) True P o s i t i ve DISEASE TOTAL TEST Diseased No diseas e Test +ve a b a+b Test -ve c d c+d TOTAL a+c b+d a+b+c +d 27 Sensitivity is how accurate the screening test is in identifying disease in people who truly have the disease.

28. “90% Sensitivity means that 90% of the diseased people screened by the test will give a “true positive” Positive test and have the disease. N e g a t i v e t e s t a nd have the disease. 28 and the remaining 10% a “false negative results”

29. The abil i ty of the t e st to correctly identify those who do not really have the disease Specificity= d/(b+d) True N e g a t ive DISEASE TOTAL TEST Diseased No d i s ea se Test +ve a b a+b Test –ve c d c+d T O T A L a+c b+d a+b+c +d 29 Specificity focuses on the accuracy of the screening test in correctly classifying truly non-diseased people. It is the probability that non-diseased subjects will be classified as normal by the screening test.

30. “ 90% Specificity means that 90% of the non diseased people screened by the test will give a “true negative” result” Negative test and do not have the disease. 30 Negative test and h a v e t he dis e a s e . “ and the remaining 10% a “false negative results”

31. Sensitivity = 80/ 100 X100= 80% Specificity = 800/ 900 X100 =88% 31

32.  When evaluating the feasibility or the success of a screening program, one should also consider the positive and negative predictive values. Positive predictive value is the probability that subjects with a positive screening test truly have the disease. Negative predictive value is the probability that subjects with a negative screening test truly don't have the disease. 32

33. Positive Predictive value Proportion of Individuals with positive testreally have the disease PPV=a/(a+b) Negative Predictive value Proportion of Individuals with negative testreally have no disease N PV = d / ( c+ d ) 33 DISEASE TOTAL TEST D is e a s e d No diseas e Test +ve a b a+b Test -ve c d c+d TOTAL a+c b+d a+b+c +d

34. Screening Test Results Diagnosis Total Diseased Not Diseases Positive 40 20 60 Negative 100 9840 9940 Total 140 9860 10,000 34 Sensitivity = 40/140 X100 = 28.57% Specificity = 9840/9860 X100 =99.79% Positive predictive value = 40/60X100 = 66.66% Negative predictive value = 9840/9940X100 = 98.9%

35. P r e v a l e nc e Increases PPV Increases; NPV Decreases Prevalence Decreases PPV Decreases; NPV Increases Specificity Increases PPV Increases Sensitivity Increases NPV Increases

36. YIELD is the amount of unrecognized disease that is detected and brought to treatment as a result of screening. YIELD = TP + FP / TP + FP + TN + FN It depends on prevalence of the disease and sensitivity of the screening test. Hence, yield of a screening test is high in high – risk screening. 36

37. Gordis, Leon. Epidemiology, 4 th Edition, Chp 5, P71-95 Park K. Textbook of preventive and social medicine; 23 rd Edition, Chp 8, P 113-119. B oni t a R , B e a gle h o l e R , Kj e ll s t r o m .T . B a s i c E p i d e m i o l o g y ; 2 nd Edition, Chp 6, P 93-96. Oxford textbook of public health, 4 th edition, Chp 12.6, P 3708- 3731. Suryakantha AH. Community medicine, Edition, Chp P. http://www.med.uottawa.ca/sim/data/Screening_e.htm http://sphweb.bumc.bu.edu/otlt/MPH- Modules/EP/EP713_Screening/EP713_Screening3.html 37

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