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Write a summary regarding impact of cut-off points in screening for diseases as caution against potential infections that can be seen in terms of sensitivity, specificity, and predictive values.
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The impact of cut-off points in screening for diseases as caution against potential infections can be seen in terms of sensitivity, specificity, and predictive values. The cut-off point should possibly be put close to point A in order to increase the sensitivity while reducing the specificity of the tests.
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essay based on the summary above. End with the sentence 'It falls under secondary prevention measures, and the effectiveness of screening is determined in terms of sensitivity, specificity, and predictive values.'
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##Introduction
Screening is one of the most important illness preventive procedures undertaken as caution against potential infections. It entails tests performed on persons without any clinical sign of disease, and although they do not diagnose illness, those who test positive are sent on further evaluation by a subsequent diagnostic test or procedure to determine whether they are infected with the disease. There are a variety of preventive measures used in curbing the onset and the overall spread of diseases. These include primary (actual prevention of disease before being able to occur), secondary (early detection of disease while its still curable, especially using the process of screening), and tertiary prevention, which limits disease spread (Hennekens, Buring, and Mayrent, 1987). The effectiveness of screening tests is defined in terms of sensitivity (the probability of possible positive result outcomes of any given test performed on a group of infected individuals), specificity (defines the probability of chances of the outcomes being negative obtained from a non-infected person) and predictive values (Anon, 2003).
##Impact of cut-off points
Moving from point A to B, all those patients without HIV are correctly identified, resulting into perfect specificity of the test results. However, at point B, the proportion of infected patients with HIV is not correctly identified, that is, the proportion is missing, resulting into reduced sensitivity of the test. At point A, it is a compromise, while at point C, there is perfect sensitivity identifying all the infected patients with HIV; however, the specificity is poor because those healthy patients are incorrectly identified as part of the infected patients with HIV. Hence, moving the cut-off from A to C increases the sensitivity while reducing the specificity of the tests. For the test, the cut-off should possibly be put close to point A. This being a compromise point, it will label patients with HIV and mislabel other patients not infected with HIV, hence minimal error at this point.
Sensitivity and specificity are inversely related in any given test because the degree of accuracy of one value increases while the other value decreases, depending on the choice of the cot-off point of any given test. Both sensitivity and specificity are used for determination of accuracy of screening tests (Grimes, Schulz, 2002).
The Blood Bank Director has to put the cut-off point for screening at point B. This is because at this point, there will be perfect specificity in identification of healthy patients, that is, those whose blood does not have the HIV antibody. However, the potential problem here is that the proportion of infected patients with HIV will not be available, a ratio of true negative test (d) / all patients without disease (d + b), i.e. d / (d + b). An investigator enrolling high-risk patients will draw the cut-off at point C. This is because of the perfect sensitivity of the test results, which identifies the population of patients infected with HIV, using the ratio; true positive test results (a)/all patients with disease (a + c), i.e. (a)/ (a + c). However, the potential problem here is the identification of healthy patients, that is, there is poor specificity of the outcome results (Anon. n.d).
##Conclusion
Screening involves procedural tests and examinations carried out on individuals who may be asymptomatic for classification purposes on the likelihood of having certain diseases. It falls under secondary prevention measures, and the effectiveness of screening is determined in terms of sensitivity, specificity, and predictive values.