When a diagnostic test is used in series mode then :
Ans. is 'b' i.e. specificity increases but the sensitivity decreases Let's first see what is meant by using a diagnostic test in 'Series mode'-It means that a particular diagnostic test (or more than one diagnostic tests) are performed sequentially.The pt. is considered positive for the diseases only when all the tests performed in the sequence give positive results.Even if one of the test is negative the pt. is considered negative for diseases.Thus as quite apparent 'serial testing' increases specificity but decreases the sensitivity.Let's also see what is Parallel testing-In parallel testing multiple diagnostic tests are given concurrently and the pt is considered positive for disease if any of the tests give positive result.For example 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) Let me explain once again -Suppose 10 different diagnostic tests are used to diagnose a particular diseaseIf test are used in Series modethe pt. will be declared positive only when all the tests give positive result.even if 9 tests give positive and one in negative pt. will be considered negative.If test are used in Parallel Modethe pt will be declared positive if any of the tests give positive result.even if 9 tests are negative and one is positive pt. will be considered positive.
Sensitivity increases but the specificity decreases
Specificity increases but the sensitivity decreases
Both sensitivity and specificity increase
Both sensitivity and specificity decrease
Screening for Disease