Reducing False-Positive Results With Fourth-Generation HIV Testing at a Veterans Affairs Medical Center
Background: In 2006, the Centers for Disease Control and Prevention issued guidelines advocating routine HIV screening for all patients. However, false-positive results are a potential patient care threat for low-risk populations even with accurate screening assays. A reduction in HIV false-positive screening results can potentially be seen by switching from the third-generation to a more sensitive and specific fourth-generation screening assay.
Methods: We studied the impact on the false-positive screening rate of a change to a fourth-generation assay at a regional US Department of Veteran Affairs Medical Center. HIV screening tests performed by the laboratory from March 1, 2016 to February 28, 2017, prior to implementation of the new assay were compared with fourth-generation HIV screening tests performed from March 1, 2017 to February 28, 2018.
Results: Of 7,516 third-generation HIV screening tests reviewed, 52 were reactive on the screening assay; 24 were true positives, 28 were false positives. The following year 7,802 fourth-generation HIV screening tests were performed and 23 were reactive on the screening assay; 16 were true positives and 7 were false positives. The positive predictive value for the third-generation test was 46% and 70% for the fourth-generation test.
Conclusions: There were fewer false-positive results with testing with the more specific fourth- vs third-generation assay (0.09% vs 0.37%, respectively), which was statistically significant ( P = .002). This reduction in false-positive screening would reduce the laboratory workload and would save an estimated $3,875 yearly and reduce the adverse effects of false-positive screening results for patients.
Veteran Population
For the general population, the fourth-generation assay has been shown to be more sensitive and specific when compared with the third-generation assay due to the addition of detection of p24 antigen and the refinement of the antigenic targets for the antibody detection.6,8,11-13,18-20,22 However, the veteran population that receives VA medical care differs significantly from the nonveteran general population. Compared with nonveterans, veterans tend to have generally poorer health status, more comorbid conditions, and greater need to use medical resources.24-26 In addition, veterans also may differ in sociodemographic status, race, ethnicity, and gender.24-26
VA research in the veteran population is unique, and veterans who use VA health care services are an even more highly selected subpopulation.26 Conclusions made from studies of the general population may not always be applicable to the veteran population treated by VA health care services due to these population differences. Therefore, specific studies tailored to this special veteran population in the specific VA health care setting are essential to ensure that the results of the general population truly and definitively apply to the veteran population.
While the false-positive risk is most closely associated with testing in a population of low prevalence, it also should be noted that false-positive screening results also can occur in high-risk individuals, such as an individual on preexposure prophylaxis (PrEP) for continuous behavior that places the individual at high risk of HIV acquisition.8,29 The false-positive result in these cases can lead to a conundrum for the clinician, and the differential diagnosis should consider both detection of very early infection as well as false positive. Interventions could include either stopping PrEP and treating for presumed early primary infection with HIV or continuing the PrEP. These interventions all have the potential to impact the patient whether through the production of resistant HIV virus due to the inadvertent provision of an inadequate treatment regimen, increased risk of infection if taken off PrEP as the patient may likely continue the behavior regardless, or the risks carried by the administration of additional antiretroviral therapies for the complete empiric therapy. Cases of an individual on PrEP who had a false-positive HIV screening test has been reported previously both within and outside the veteran population.8 Better screening tests with greater sensitivity/specificity can only help in guiding better patient care.
Limitations
This quality assurance study was limited to retrospectively identifying the improvement in the false-positive rate on the transition from the third-generation to the more advanced fourth-generation HIV screen. False-positive screen cases could be easily picked up on review of the confirmatory testing per the CDC laboratory HIV testing algorithm.12,13 This study also was a retrospective review of clinically ordered and indicated testing; as a result, without confirmatory testing performed on all negative screen cases, a false-negative rate would not be calculable.
This study also was restricted to only the population being treated in a VA health care setting. This population is known to be different from the general population.24-26
Conclusions
The switch to a fourth-generation assay resulted in a significant reduction in false-positive test results for veteran patients at CMJCVAMC. This reduction in false-positive screening not only reduced laboratory workload due to the necessary confirmatory testing and subsequent review, but also saved costs for technologist’s time and reagents. While this reduction in false-positive results has been documented in nonveteran populations, this is the first study specifically on a veteran population treated at a VAMC.8,11,18 This study confirms previously documented findings of improvement in the false-positive rate of HIV screening tests with the change from third-generation to fourth-generation assay for a veteran population.24
