to nbme9999 -- can you explain this? - drmaafo

[ArchivalUser]

A 24-year-old man and a 22-year-old woman come to the office for the first time for premarital evaluation and counseling. Neither of them has ever been sexually active, because they "want to wait" until after marriage to have sexual intercourse. Other discussion reveals that they have never had blood transfusions, used illicit drugs, or drunk excessive amounts of alcohol. They have heard about the test for HIV antibody, and wonder whether they should obtain this test before marriage. Compared with persons who have multiple risk factors for HIV, which of the following statements best applies to this couple?

A) The negative predictive value of the test would be lower B) The positive predictive value of the test would be lower C) The sensitivity of the test would be higher D) The sensitivity of the test would be lower E) The specificity of the test would be lower

[ArchivalUser]

The answer is B


If the disease has a high prevalence ( high HIV in multiple sexual partner ), every positive result would be a true positive. There could be no false positive results, and the PPV would be 100%.
In a low prevalence disease as in this situation, PPV would be low, and the chance of false positive increase.

[ArchivalUser]

SUPER THANKS!

[ArchivalUser]

The concept here
Higher prevalence increases positive predictive value. Conversely, increased prevalence results in decreased negative predictive value