When a diagnostic test is used in series mode then -
Ans. is 'b' i.e., Specificity increases but the sensitivity decreases Diognostic test in 'Series mode '- It means that a paicular diagnostic test (or more than one diagnostic tests) are performed sequentially. The pt . is considered positve for the diseases only when all the tests performed in the sequence give positive results. o Even if one of the test is negative the pt. is considered negative for diseases. o Thus as quite apparent 'serial testing' increases specificity but decreases the sensitivity. Parallel testing? In parallel testing multiple diognostic tests are given concurrently and the pt is considered positive for disease if any of the tests give positive result. o For exmaple ECG and Echocardiography are two procedures used in the diagnosis of VSD. When used in Parallel mode the pt. will be considered to have VSD, if any of the test give positive result (even if the other test gives negative result) For example Suppose 10 different diagnostic tests are used to diagnose a paicular disease If test are used in Series mode The pt. will be declared positive only when all the tests give positive result. o Even i f 9 tests give positive and one in negative pt. will be considered negative. o Because even a single positive test is considered positive True positivity increases --) Sensitivity increases. If test are used in Parallel Mode the pt will be declared positve if any of the tests give positive result. even i f 9 tests are negative and one is positive pt. will be considered positive. o As, even a single negative test rules out the disease Increase in true negative rate Specificity increases. Multiple Diagnostic tests Series Mode Parallel Mode Decreased sensitivity o Increased sensitivity Increased specificity o Decreased specificity Increased positive predictive value o Increased negative predictive value
Sensitivity increases but the specificity decreases
Specificity increases but the sensitivity decreases
Both sensitivity and specificity increase
Both sensitivity and specificity decrease