<prompt> 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 valueacaabbc  <response>: Both options a b are correct because by using a diagnostic test in series mode, following parameters are affected:-i Specificity Increasedii PPV Increasediii Sensitivity DecreasedBut, 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. 