RPR tests for syphilis have a

The positive predictive value of 0.054% suggests that, if aperson is tested positive, the probability that he/she will havesyphilis is 0.00054. If a person is tested negative, according tothe negative predictive value, the probability that he/she willhave syphilis is 0.9999. This means that the test can predict withgreat accuracy if a person is not having syphilis, but the testpredicting that a person is having syphilis is unreliable. In thisscenario, the best way to use the test on general public is toexclude those one from further tests if one is tested negative byconcluding that a negative test means that person is not having thedisease. So, screening is to find out from the general population,a smaller group of people, who have higher probability of havingthe disease. Then in this smaller subset, detailed tests shall beconducted identify the presence of disease.

The reason why we are getting such results from the test isbecause of the fact that the prevalence rate of the disease in verylow. In absolute numbers if we see, we get a large number of falsepositive results from the test, where as there is a very smallnumber of results that are false negative.