Results
From March 1, 2016 to February 28, 2017, 7,516 specimens were screened for HIV, using the third-generation assay, and 52 specimens tested positive for HIV. On further review of these reactive specimens per the CDC laboratory testing algorithm, 24 tests were true positive and 28 were false positives with a PPV of 46% (24/52) (Figure 1).
From March 1, 2017 to February 28, 2018, 7,802 specimens were screened for HIV using a fourth-generation assay and 23 tested positive for HIV. On further review of these reactive specimens per the CDC laboratory testing algorithm, 16 were true positive and 7 were false positives with a PPV of 70% (16/23).
The fourth-generation assay was more specific when compared with the third-generation assay (0.09% vs 0.37%, respectively) with a 75.7% decrease in the false-positivity rate after the implementation of fourth-generation testing. The decreased number of false-positive test results per month with the fourth-generation test implementation was statistically significant (P = .002). The mean (SD) number of false-positive test results for the third-generation assay was 2.3 (1.7) per month, while the fourth-generation assay only had a mean (SD) of 0.58 (0.9) false positives monthly. The decrease in the percentage of false positives per month with the implementation of the fourth-generation assay also was statistically significant (P = .002) (Figure 2).
For population-based reference of the tested population at CMJCVAMC, there was a FileMan search for basic demographic data of patients for the HIV specimens screened by the third- or fourth-generation test (Table). For the population tested by the third-generation assay, 1,114 out of the 7,516 total tested population did not have readily available demographic information by the FileMan search as the specimens originated outside of the facility. For 6,402 of 7,516 patients tested by the third-generation assay with demographic information, the age ranged from 25 to 97 years with a mean of 57 years. This population of 6,402 was 88% male (n = 5,639), 50% African American (n = 3,220) and 43% White (n = 2,756). For the population tested by the fourth-generation assay, 993 of 7,802 total tested population did not have readily available demographic information by the FileMan search as the specimens originated outside of the facility. For the 6,809 of 7,802 patients tested by the fourth-generation assay with demographic information, the age ranged from 24 to 97 years with a mean age of 56 years. This population was 88% male (n = 5,971), 47% African American (n = 3,189), and 46% White (n = 3,149).
Discussion
Current practice guidelines from the CDC and the US Preventive Services Task Force recommend universal screening of the population for HIV infection.5,6 As the general population to be screened would normally have a low prevalence of HIV infection, the risk of a false positive on the initial screen is significant.17 Indeed, the CMJCVAMC experience has been that with the third-generation screening assay, the number of false-positive test results outnumbered the number of true-positive test results. Even with the fourth-generation assay, approximately one-third of the results were false positives. These results are similar to those observed in studies involving nonveteran populations in which the implementation of a fourth-generation screening assay led to significantly fewer false-positive results.18