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Analysis of the optimal cut-point for HIV-p24 antigen testing to diagnose HIV infection in HIV-exposed children from resource-constrained settings

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Abstract

Background

Nucleic-acid-testing (NAT) to diagnose HIV infection in children under age 18 months provides a barrier to HIV-testing in exposed children from resource-constrained settings. The ultrasensitive HIV-p24-antigen (Up24) assay is cheaper and easier to perform and is sensitive (84–98%) and specific (98–100%). The cut-point optical density (OD) selected for discriminating between positive and negative samples may need assessment due to regional differences in mother-to-child HIV-transmission rates.

Objectives

We used receiver operator characteristics (ROC) curves and logistic regression analyses to assess the effect of various cut-points on the diagnostic performance of Up24 for HIV-infection status among HIV-exposed children. Positive and negative predictive values at different rates of disease prevalence were also estimated.

Study design

A study of Up24 testing on dried blood spot (DBS) samples collected from 278 HIV-exposed Haitian children, 3–24-months of age, in whom HIV-infection status was determined by NAT on the same DBS card.

Results

The sensitivity and specificity of Up24 varied by the cut-point-OD value selected. At a cut-point-OD of 8-fold the standard deviation of the negative control (NCSD), sensitivity and specificity of Up24 were maximized [87.8% (95% CI, 83.9–91.6) and 92% (95% CI, 88.8–95.2), respectively]. In lower prevalence settings (5%), positive and negative predictive values of Up24 were maximal (75.9% and 98.8%, respectively) at a cut-point-OD that was 15-fold the NCSD.

Conclusions

In low prevalence settings, a high degree of specificity can be achieved with Up24 testing of HIV-exposed children when a higher cut-point OD is used; a feature that may facilitate more frequent use of Up24 antigen testing for HIV-exposed children.

Section snippets

Background

The World Health Organization recommends highly active antiretroviral therapy (HAART) for all children diagnosed with HIV infection at two years of age and younger.1 HAART for HIV-infected children in resource-constrained settings (RCSs) is hindered by limited access to nucleic acid testing (NAT) required for diagnosis. Frequent HIV-testing of infants with ongoing exposure to HIV through breast-feeding is also deterred. Evaluation of ultrasensitive p24 (Up24) antigen assays on liquid or dried

Objective

We used receiver operator characteristics (ROC) curves and logistic regression analyses to assess the effect of various cut-points on the diagnostic performance of Up24 to correctly classify HIV-infection status among HIV-exposed children. Positive and negative predictive values at different rates of disease prevalence were also estimated.

Study design

As part of the JHPIEGO-UNICEF and Caris, Early Infant Diagnosis (EID) program in Haiti, DBS (Whatman # 903 cards; Fischer Scientific, MA) were collected on 278 HIV-exposed, Haitian children between 0.1 and 24 months of age for testing by HIV DNA polymerase chain reaction (HIV-DNA PCR; AMPLICOR HIV-1 DNA test version 1.5; Roche Diagnostics GMBH, Germany). Testing was done in a laboratory in Kenya accredited for infant HIV testing. This laboratory also participates in an external quality

Results

The cohort of 278 children were at a median age of four months (IQR: 2.0–7.7 months) at the time of DBS collection. Samples were stored for a median of 14 months (IQR: 11.4–15.7 months; range 7–26 months) before testing with the Up24 assay. The HIV-infection prevalence was 14.7% by HIV-DNA PCR testing. The median age of the 41 HIV-infected infants was four months (IQR: 2.2–7.4 months).

Fig. 1 shows the distribution of adjusted OD values for HIV-exposed children who tested positive or negative by

Discussion

In this study of 278 HIV-exposed children for whom the prevalence of HIV infection was determined at 14.5% by HIV-DNA PCR, we found that the sensitivity and specificity of Up24 testing on DBS samples varied significantly based on the cut-point selected. When the Youden index (8-fold NCSD) was used, sensitivity and specificity of Up24 was 88% and 92%, respectively. The cut-point identified by ROC curves was similar to that identified using AUC and logistic regression analyses. By increasing the

Conflicts of interest

The authors do not have an association that might pose a conflict of interest.

Sources of financial support

This work was funded by ICTR award (D.P.) made possible through grant number UL1 RR 025005 from the National Center for Research Resources (NCRR), a component of the National Institutes of Health (NIH), and NIH Roadmap for Medical Research. Its contents are solely the responsibility of the authors and do not necessarily represent the official view of NCRR or NIH”. The work was also supported by the National Institutes of Health grant # R01HD057784 (D.P.).

Acknowledgments

We thank the study participants, the Haitian Ministry of Health, and the CARIS Foundation for making this study possible. The study was approved by the Institutional Review Board at Johns Hopkins University with waiver of consent, and also by the Haitian Ministry of Health and the CARIS Foundation, the EID implementing partner.

References (20)

  • M.C. Knuchel et al.

    Ultrasensitive quantitative HIV-1 p24 antigen assay adapted to dried plasma spots to improve treatment monitoring in low-resource settings

    J Clin Virol

    (2006)
  • V. Mwapasa et al.

    Using a simplified human immunodeficiency virus type 1 p24 antigen assay to diagnose pediatric HIV-infection in Malawi

    J Clin Virol

    (2010)
  • T. Fawcett

    An introduction to ROC analysis

    Pattern Recognit Lett

    (2006)
  • Antiretroviral therapy for HIV infection in infants and children: towards universal access

    (2010)
  • A.J. De Baets et al.

    Pediatric human immunodeficiency virus screening in an African district hospital

    Clin Diagn Lab Immunol

    (2005)
  • S.A. Fiscus et al.

    Ultrasensitive p24 antigen assay for diagnosis of perinatal human immunodeficiency virus type 1 infection

    J Clin Microbiol

    (2007)
  • E. George et al.

    Potential of a simplified p24 assay for early diagnosis of infant human immunodeficiency virus type 1 infection in Haiti

    J Clin Microbiol

    (2007)
  • R.A. Respess et al.

    Evaluation of an ultrasensitive p24 antigen assay as a potential alternative to human immunodeficiency virus type 1 RNA viral load assay in resource-limited settings

    J Clin Microbiol

    (2005)
  • J. Schupbach et al.

    Sensitive detection and early prognostic significance of p24 antigen in heat-denatured plasma of human immunodeficiency virus type 1-infected infants

    J Infect Dis

    (1994)
  • R. Sutthent et al.

    p24 antigen detection assay modified with a booster step for diagnosis and monitoring of human immunodeficiency virus type 1 infection

    J Clin Microbiol

    (2003)
There are more references available in the full text version of this article.

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    In this group, molecular tests such as proviral DNA-based or HIV-1 RNA assays are best. In resource-poor settings, ultrasensitive p24 antigen has been used on dried blood spots in Tanzania and Haiti.47,48 In this test the sample is heat denatured and then tested with an immunoassay.

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