Clinical application evaluation of two fourth-generation human immunodeficiency virus (HIV) screening assays in West China Hospital

A method to alleviate false-positive results of the Elecsys HIV combi PT assay

To explore the effects of urea dissociation on reducing false-positive results of  the Elecsys HIV combi PT assay. A retrospective analysis was used to evaluate the false-positive rate of the Elecsys HIV combi PT assay. Six false-positive sera, six positive sera and six sera from patients with early HIV infection were collected. Dissociation was performed using 1 mol/L, 2 mol/L, 4 mol/L, 6 mol/L, or 8 mol/L urea, and HIV screening assay were then detected to select the appropriate concentration of urea dissociation. Next, 55 false-positive sera and 15 sera from early HIV infection were used to verify the best concentration of urea to achieve dissociation. Retrospective analysis showed that the COI of the Elecsys HIV combi PT assay in false-positive sera ranged from 1.0 to 200.0, and approximately 97.01%(227/234) of false-positive sera were in the range of 1.0-15.0. The avidity index (AI) in positive and false-positive sera decreased as the urea dissociation concentration increased. When the dissociation concentration was 6 mol/L, the AI of false-positive serum was between 0.0234 and 0.2567, and the AI of early HIV infection sera was between 0.4325 and 0.5017. The difference in AI between false-positive and positive samples was significant. When negativity was defined as an AI of less than 0.3970, the sensitivity and specificity were 100.0% and 100.0%, respectively. Urea-mediated dissociation could significantly reduce the false-positive rate of the Elecsys HIV combi PT assay with a low COI. Our findings provided a reference for distinguishing positive and false-positive of the Elecsys HIV combi PT assay.

The evaluation of low cut-off index values of Elecsys® HIV combi PT assay in predicting false-positive results

Objective

To analyze the results of different cut‐off index (COI) values of Elecsys^® HIV combi PT assay and to assess the role of COI in reducing the frequency of false‐positive results.

Methods

We conducted a retrospective study of samples analyzed by Elecsys^® HIV combi PT assay, a 4th‐generation ECLIA, between 2016 and 2017. A total amount of 379 122 samples were collected for HIV (Human Immunodeficiency Virus) screening.

Results

A total of 379 122 samples were analyzed. 2528 (0.67%) were positive by Elecsys^® HIV combi PT. Of these, 468 were false‐positive results, and most of them (94.87%) were in samples with 1 < COI < 15. The false‐positive rate was 0.12%. Patients with false‐positive samples were more distributed in elder (P < .001) and female (P < .001) than true‐positive specimens. The median COI in true‐positive specimens was (385.20), which is significantly higher than false‐positive specimens (2.08). The consistency between Elecsys^® HIV combi PT assay and 3rd‐generation and positive predictive value (PPV) increased with higher COI values. Cancer, infection, and neurological diseases were considered the potential confounding factors of HIV false‐positive results (19.44%, 11.11%, and 6.62%, respectively).

Conclusion

Samples with low COI values, especially those contain confounding factors, need to be further scrutinized to determine whether the confounding factors may cause false‐positive problem. In addition, the hypothesis that low COI values may predict false‐positive results is valid.

Diagnosis and treatment of diffusible Penicillium marneffei in human immunodeficiency virus-negative patients: A challenge for the physician

Penicillium marneffei infection in human immunodeficiency virus (HIV)-negative patients is addressed far less often. In this article, a small cohort of HIV-negative patients who disseminated P. marneffei infection was included. Sites of infection were found from blood culture, as subcutaneous nodules, or from lymph node biopsy. Fever, rash, swollen lymph nodes, anaemia and weight loss were common characteristics in most infected patients. The signs and symptoms are diverse and create challenges for accurate diagnosis. This paper will assist our understanding of this disease and contribute to an appropriate regime of therapy, thus improving the health of P. marneffei-positive patients.

Specificity of two HIV screening tests detecting simultaneously HIV-1 p24 antigen and antibodies to HIV-1 and -2

This study aimed at assessing the specificity of the Elecsys^® HIV combi PT in comparison to the ARCHITECT^® HIV Ag/Ab Combo. With both of these assays, 3997 unselected sera from patients of a tertiary health care centre in Basel, Switzerland, were screened for HIV. Reactive sera were reanalysed on the VIDAS^® HIV Duo Ultra to identify false-reactive specimens prior to confirmation by quantitative PCR and line immunoassay. The Elecsys^® compared to the ARCHITECT^® shows a similar specificity (99.7% versus 99.8%) but a slightly lower positive predictive value (71.8% versus 80%). Samples tested with a cut-off index (COI) between 0.91 and 4.85 (cut-off <0.9) with the Elecsys^® and with a signal to cut-off index (S/CO) between 1.09 and 12.49 (cut-off <1.0) with the ARCHITECT^® were false-reactive. There was no false-reactive result with the VIDAS^®. Of the false-reactive samples, 66.7% could be related to patient-specific underlying conditions. The HIV two-tiered diagnostic algorithm proposed in this work improved the positive predictive values of the Elecsys^® or ARCHITECT^® to 100% when the results of the VIDAS^® were included. Values just above the cut-off are highly suspicious to be false-reactive and high COI or S/CO ratios are associated with true positivity.