In a surveillance centre for Hepatitis , in a low prevalance area, the method for testing for Hepatitis B was single ELISA. This policy was changed to double testing in series. This would result in the following 2 parameters of the test being affected -a) Specificity and positive predictive valueb) Sensitivity and positive predictive valuec) Sensitivity and negative predictive valued) Specificity and negative predictive value

Both options 'a' & 'b' are correct because by using a diagnostic test in series mode, following parameters are affected:- i) Specificity → Increased ii) PPV → Increased iii) Sensitivity → Decreased But, the main purpose of a test to use in series is to increase the specificity and positive predictive value test. As specificity increases sensitivity decreases inevitably (has been explained previously). So, more appropriate answer is 'a' i.e., specificity and positive predictive value.