Distinguish Between Screening Test and Diagnostic Tests

A diagnostic test is any kind of medical test performed to aid in the diagnosis of detection of a suspected disease or condition. This is different from a screening test which is used when not when a disease or condition is suspected, but when people are considered to be at high risk of developing a disease or condition. Diagnostic test are usually performed after a positive screening test to establish a definitive diagnosis.They are also offered to individuals who have some indication, be it a symptom, sign or a history of a particular disease or condition. For example; a physician performing a biopsy on a woman with a lump in one of her breasts is a diagnostic test for suspected breast cancer. A post-menopausal woman undergoing a routine mammogram without any breast cancer symptoms is a screening test for breast cancer. Screening tests are offered to asymptomatic people who may or may not have early disease or disease precursors and test results are used to guide whether or not a diagnostic test should be offered.Diagnostic tests are offered to people who have a specific indication of possible illness (a history, symptom, sign or positive screening test result) to determine whether or not they have the disease in question. Also, a screening test helps to identify individuals who are not exhibiting any symptoms (asymptotic) and determine if they are at risk of developing a disease or condition. Characteristics of a Diagnostic Test * The cutoff for a positive result is precisely defined, with stress being laid on diagnostic precision and accuracy * They cost more because of the accuracy that is required. * The test provides for a definitive diagnosis The test is often invasive, such as a lumbar puncture to test for meningitis * They are used for individuals who are symptomatic Characteristics of a Screening Test * The cutoff for a positive result is extremely sensitive and may result in numerous false positives * The cost is usually low, since the accuracy is low * The test results determine the level of risk and whether a diagnostic test is required * The tests are usually non-invasive * They are used for high risk individuals who are asymptomatic Differences between diagnostic tests and screening tests [1]. |  Diagnostic test|  Screening test|Result| The cutoff is set towards high specificity, with more weight given to diagnostic precision and accuracy than to the acceptability of  the test to patients| The cutoff is set towards high sensitivity. As a result many of the positive results are false positives. This is acceptable, particularly if the screening test is not harmful or expensive. | Cost| Patients have symptoms that require accurate diagnosis and therefore higher costs are justified. | Since large numbers of people will be screened to identify a very small number of cases, the financial resources needed must be justified carefully. Result of the test| The test provides a definitive diagnosis (e. g. a definite diagnosis of Meningitis through blood test or lumbar puncture. | The result of the test is an estimate of the level of risk and determines whether a diagnostic test is justified. | Invasiveness| May be invasive (lumbar puncture)| Often non-invasive. | Population offered the test| Those with symptoms or who are under investigation following a positive screening test. | Those at some risk but without symptoms of disease. |

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