04-04-2016, 01:42 PM
A test is being devised to screen for human immunodeficiency virus (HIV). Before it is approved for use in the community, it is tested in a population of people, 40% of whom are known to be HIV positive by the Western blot test (gold standard). This new test turns out to be positive in only 50 percent of people who are known to have HIV, while it is negative in 30% of those who do not have the disease. What statement is true regarding the characteristics of this screening test?
A. 30% of the people who do not have the disease will test negative on the test
B. 30% of the people who have the disease will be tested positive for the disease by this test
C. 32% percent of people who test positive on the new test actually have the disease
D. 40% of the people who do not have the disease will be correctly identified as negative for the disease by this test
E. 60% of people who test positive on the new test actually have the disease
A family practice physician is collecting information for a report he is preparing for the other members of his group practice to determine if they should change their current human immunodeficiency virus (HIV) screening protocols. Currently, for all patients requesting testing and with no signs of infection, the screening test is an enzyme-linked immunosorbent assay (ELISA) that detects anti-HIV antibodies. Positive tests are followed-up with a confirmatory Western blot. The screening test under consideration to replace the current test also detects anti-HIV antibodies and is more expensive. It is, however, more sensitive overall and more likely to detect infections in the 2 to 6-week postexposure period. For determination of prevalence and incidence rates, the physician determines the total number of asymptomatic patients requesting testing by the practice and the total who subsequently undergo confirmatory Western blot testing over the past 5 years.
Item 1 of 3
Assuming that the true incidence and prevalence rates for this patient population remains constant, what is an accurate conclusion based on the information provided?
A. The new test will result in a higher total number of positive confirmatory Western blot results for the same number of tested patients
B. The new test will result in a lower total number of negative confirmatory Western blot results for the same number of tested patients
C. Use of the new test for screening will result in a higher percentage of true positives
D. Use of the new test for screening will result in a higher percentage of false positives
E. Use of the newer test will result in a higher total number of Western blots required for confirmation of results for the same number of tested patients
Item 2 of 3
The physician determines that over the past 5 years, the group has provided testing for 1000 asymptomatic individuals. Ten of these tests were positive. In the table below are relevant data for the current enzyme-linked immunosorbent assay (ELISA) screening test and the new ELISA screening test under evaluation.
Screening test Cost per test Test sensitivity Test specificity
Current ELISA test $5 98% 95%
New ELISA test $10 99% 90%
Assuming that true incidence rate for the tested patient population remains unchanged, what conclusion can the physician draw from this information?
A. The minimum cost (not including confirmatory testing) to detect one additional true HIV infection is approximately $500
B. The minimum cost (not including confirmatory testing) to detect one additional true HIV infection is approximately $50
C. The minimum cost (not including confirmatory testing) to detect one additional true HIV infection is approximately $5000
D. The minimum cost (not including confirmatory testing) to detect one additional true HIV infection is approximately $50,000
E. The minimum cost (not including confirmatory testing) to detect one additional true HIV infection is approximately $500,000
Item 3 of 3
The physician also is considering the possibility of submitting blood samples of all asymptomatic patients requesting testing to a regional laboratory that will run monthly pooled western blot testing of the blood samples. Should the pooled sample indicate human immunodeficiency virus (HIV) infection, the group will be notified and they would then conduct a virtually 100% sensitive HIV nucleic acid amplification test (NAAT) of all patients whose blood was included in the pooled test. Based only on this information, what is a primary advantage to this addition to a potential screening protocol?
End of set
A. The maximum total number of required western blots will be reduced to 12 per year
B. The new protocol likely will detect more patients with early (0-2 months) HIV infection
C. The new protocol will virtually eliminate the probability of a false positive HIV NAAT test
D. The new protocol would provide a strong indication for work-up of occult serious non-HIV disease in patients whose pooled blood sample was positive and whose HIV NAAT test is negative
E. The protocol will eliminate the need for additional initial screening testing
A. 30% of the people who do not have the disease will test negative on the test
B. 30% of the people who have the disease will be tested positive for the disease by this test
C. 32% percent of people who test positive on the new test actually have the disease
D. 40% of the people who do not have the disease will be correctly identified as negative for the disease by this test
E. 60% of people who test positive on the new test actually have the disease
A family practice physician is collecting information for a report he is preparing for the other members of his group practice to determine if they should change their current human immunodeficiency virus (HIV) screening protocols. Currently, for all patients requesting testing and with no signs of infection, the screening test is an enzyme-linked immunosorbent assay (ELISA) that detects anti-HIV antibodies. Positive tests are followed-up with a confirmatory Western blot. The screening test under consideration to replace the current test also detects anti-HIV antibodies and is more expensive. It is, however, more sensitive overall and more likely to detect infections in the 2 to 6-week postexposure period. For determination of prevalence and incidence rates, the physician determines the total number of asymptomatic patients requesting testing by the practice and the total who subsequently undergo confirmatory Western blot testing over the past 5 years.
Item 1 of 3
Assuming that the true incidence and prevalence rates for this patient population remains constant, what is an accurate conclusion based on the information provided?
A. The new test will result in a higher total number of positive confirmatory Western blot results for the same number of tested patients
B. The new test will result in a lower total number of negative confirmatory Western blot results for the same number of tested patients
C. Use of the new test for screening will result in a higher percentage of true positives
D. Use of the new test for screening will result in a higher percentage of false positives
E. Use of the newer test will result in a higher total number of Western blots required for confirmation of results for the same number of tested patients
Item 2 of 3
The physician determines that over the past 5 years, the group has provided testing for 1000 asymptomatic individuals. Ten of these tests were positive. In the table below are relevant data for the current enzyme-linked immunosorbent assay (ELISA) screening test and the new ELISA screening test under evaluation.
Screening test Cost per test Test sensitivity Test specificity
Current ELISA test $5 98% 95%
New ELISA test $10 99% 90%
Assuming that true incidence rate for the tested patient population remains unchanged, what conclusion can the physician draw from this information?
A. The minimum cost (not including confirmatory testing) to detect one additional true HIV infection is approximately $500
B. The minimum cost (not including confirmatory testing) to detect one additional true HIV infection is approximately $50
C. The minimum cost (not including confirmatory testing) to detect one additional true HIV infection is approximately $5000
D. The minimum cost (not including confirmatory testing) to detect one additional true HIV infection is approximately $50,000
E. The minimum cost (not including confirmatory testing) to detect one additional true HIV infection is approximately $500,000
Item 3 of 3
The physician also is considering the possibility of submitting blood samples of all asymptomatic patients requesting testing to a regional laboratory that will run monthly pooled western blot testing of the blood samples. Should the pooled sample indicate human immunodeficiency virus (HIV) infection, the group will be notified and they would then conduct a virtually 100% sensitive HIV nucleic acid amplification test (NAAT) of all patients whose blood was included in the pooled test. Based only on this information, what is a primary advantage to this addition to a potential screening protocol?
End of set
A. The maximum total number of required western blots will be reduced to 12 per year
B. The new protocol likely will detect more patients with early (0-2 months) HIV infection
C. The new protocol will virtually eliminate the probability of a false positive HIV NAAT test
D. The new protocol would provide a strong indication for work-up of occult serious non-HIV disease in patients whose pooled blood sample was positive and whose HIV NAAT test is negative
E. The protocol will eliminate the need for additional initial screening testing