What would be the impact of moving the cut-off line from A to C on sensitivity and specificity?

Infection with the human immunodeficiency virus (HIV) is routinely diagnosed by detecting the presen Show more Infection with the human immunodeficiency virus (HIV) is routinely diagnosed by detecting the presence of specific antibodies in the patients serum. Although the presence of the virus itself can be now be detected these tests remain expensive and require laboratory techniques that are not routinely available. The diagnosis of HIV infection begins with an enzyme immunoassay (EIA). The optical density (OD) of the patients EIA is compared to a control specimen (OD ratio). If the OD ratio is above the established cutoff for that control sample on repeat testing the specimen is termed repeatedly reactive. The EIA is relatively sensitive fast simple and inexpensive which makes it an appropriate screening test. However if one examines the ODs for a large group of samples from patients with and without true HIV infection you can see that there is some overlap in their EIA results if a value of A is used for the cutoff: Hypothetical distribution of OD ratios for patients with and without HIV infection. Patients with HIV infection are depicted with the BLUE thick line and the patients without HIV are depicted with a thin RED line. 1. What would be the impact of moving the cut-off line from A to B on sensitivity and specificity? 2. What would be the impact of moving the cut-off line from A to C on sensitivity and specificity? 3. Where would you suggest setting the cut-off? 4. If you are the director of a blood bank and having HIV-negative blood is vital where would you set the cut-off and why? 5. If you are the director of an investigational drug for HIV-positive patients which decrease viral load and protect T cells BUT have significant side-effects where would you set the cut-off and why? Show less