Correspondence

Early Detection of HIV in Neonates

N Engl J Med 1993; 329:60-62July 1, 1993

Article

To the Editor:

Miles et al. (Feb. 4 issue)1 suggest that the immune-complex-dissociated HIV p24 antigen assay may be of value in the early diagnosis of pediatric human immunodeficiency virus (HIV) infection. We do not believe that the data they present adequately support this conclusion. The relative benefit of dissociation cannot be established, since the results of HIV p24 antigen detection in the untreated samples were not reported. A blocking assay was not performed to confirm the positive results that were observed not only in infected infants but also in 2 of 22 uninfected infants. The number of children studied during the first 2 months of life, when the diagnosis of HIV infection is most critical, is unclear; the median age of the group of 78 children was 3.6 years (range, 6 days to 13 years).

In an ongoing prospective study of infants born to HIV-seropositive women, we evaluated p24 antigen detection with and without immune-complex dissociation for the diagnosis of HIV infection. Samples from 15 infected infants (72 samples) and 26 uninfected infants (100 samples) were tested for HIV p24 antigen (HIVAG-1, Abbott Laboratories, Abbott Park, Ill.). For dissociation, specimens were treated with glycine buffer, followed by neutralization with TRIS base. All positive reactions obtained before treatment were confirmed by a blocking assay. After dissociation, positive reactions were confirmed only if the result before treatment had been negative. The HIV status of the children was determined by isolation of virus.

Before dissociation, p24 antigen was detected in 8 (53 percent) of 15 HIV-infected infants studied in the first two months of life. It was detected in 11 of these children (73 percent) later in the first year of life. After dissociation, reactivity decreased in five serum samples and increased in eight. For six of the samples in which reactivity increased, the sample:cutoff ratio, a measure of optical density that is used in reporting the results of enzyme-linked immunoassays, changed from negative to weakly positive (range, 1.04 to 2.72) after treatment. Two of these six results were confirmed by neutralization; one was not reproducible, and three could not be confirmed because the volume of serum was insufficient.

Two of four serum samples from one additional neonate became p24 antigen-reactive after dissociation of immune complexes during the first two months of life; insufficient serum volume precluded confirmation of this result. Another child, who became negative for p24 antigen after two months, remained transiently positive only after immune-complex dissociation. All 100 samples from 26 uninfected infants were antigen-negative both before and after treatment.

Our results suggest that the gain in the detection of HIV p24 antigen after immune-complex dissociation is small, notably during the first two months of life. In addition, protein denaturation through acid treatment of specimens may influence the reproducibility of the assay, making confirmation of reactive samples essential. In this context, the performance of kits for the detection of HIV p24 antigen should be carefully assessed before the issue of immune-complex dissociation in neonatal diagnosis is resolved.

Micheline Fauvel, M.Sc.
Laboratoire de Sante Publique du Quebec, Ste-Anne-de-Bellevue, QC H9X 3R5, Canada

Denis Henrard, Ph.D.
Abbott Laboratories, Abbott Park, IL 60064

Gilles Delage, M.D.
Societe Canadienne de la Croix-Rouge, Montreal, QC H1W 1B2, Canada

Normand Lapointe, M.D., M.Sc.
Centre Maternel et Infantile sur le SIDA, Hopital Sainte-Justine, Montreal, QC H3T 1C5, Canada

1 References

1. 1

   Miles SA, Balden E, Magpantay L, et al. Rapid serologic testing with immune-complex-dissociated HIV p24 antigen for early detection of HIV infection in neonates. N Engl J Med 1993;328:297-302
   Full Text | Web of Science | Medline

To the Editor:

Miles et al. found that five of eight cord-blood samples from neonates with proved HIV infection were positive when tested with an immune-complex-dissociated p24 antigen assay. Two additional children tested positive within the first month of life. There were 2 false positive results among the 22 cord-blood samples from HIV-negative infants. Unfortunately, the investigators did not present comparable data for the regular p24 antigen assay.

We tested 81 children born to HIV-infected mothers (21 of whom were infected, 24 of whom were seronegative after testing positive, and 36 whose status remains indeterminate) using regular and immune-complex-dissociated HIV antigen (Abbott HIVAG-1 and Abbott Immune Complex Disruption Assay). Our results in general support the findings of Miles et al (Table 1Table 1Comparison of Assays for the Diagnosis of HIV in Children.). In most cases the children were tested on multiple occasions. All were tested with HIV culture and the p24 antigen assay. Because samples were insufficient in many cases, not all specimens were tested for immune-complex-dissociated HIV antigen.

In our limited experience and contrary to other reports,1 HIV antigen detection has been quite sensitive in infected infants less than three months old (sensitivity, 100 percent for both the regular and the immune-complex-dissociated assays). In babies 4 to 12 months of age the regular assay was 60 to 70 percent sensitive, whereas the immune-complex-dissociated assay was 100 percent sensitive. After one year of age, both assays had a sensitivity of 40 to 50 percent. To date we have not identified any false positive results of either assay in any age group. Decreases in antigenemia with age may be due to decreases in viral load attributable to antiretroviral chemotherapy or to better recognition and containment of virus with the maturation of the infant's immune system.

The use of cord blood is tempting, since it is easy to obtain in large quantities. But false positive reactions are a source of concern. Such reactions may be due either to contamination with maternal blood during the collection of samples or to a higher background associated with the Coulter immune-complex-dissociated assay (Coulter Immunology, Hialeah, Fla.) (Fiscus SA: unpublished data). We caution against the use of cord blood in the diagnosis of pediatric HIV infection. We also recommend two positive results (of culture, HIV antigen assay, immune-complex-dissociated HIV antigen assay, or polymerase chain reaction) in two separate samples of peripheral blood for a definitive diagnosis.

Susan A. Fiscus, Ph.D.
Pietro Vernazza, M.D.
Wilma Lim, M.D.
University of North Carolina at Chapel Hill, Chapel Hill, NC 27599

1 References

1. 1

   Borkowsky W, Krasinski K, Paul D, et al. Human immunodeficiency virus type 1 antigenemia in children. J Pediatr 1989;114:940-945
   CrossRef | Web of Science | Medline

Author/Editor Response

The authors reply:

To the Editor: We appreciate the two responses. We, too, have used the regular HIV p24 antigen test (Abbott) to analyze many of these same samples. For the 7 HIV-infected neonates we described, we found that 14 of 17 samples were positive by immune-complex-dissociated p24 antigen assay (Coulter) but only 3 of 14 were positive by the regular assay. Three samples were not tested. All these results were confirmed by neutralization. In our experience, there is a clear increase in the sensitivity of antigen testing in infants after immune-complex dissociation.

We agree with the authors of the letters that these results are early and await confirmation from several of the large, prospective cohort studies now under way. In addition, there are at least four methods of immune-complex disruption, and the relative efficacy of each remains to be seen. As a consequence, we echo the recommendation of Fiscus et al. that two positive results from different tests of two separate samples of blood be required before a definitive diagnosis of HIV infection is made.

Steven A. Miles, M.D.
Yvonne Bryson, M.D.
University of California, Los Angeles, Los Angeles, CA 90024

Citing Articles (2)

Citing Articles

1. 1

   Valerio Del Bono, Roberto Biselli, Roberto Nisini, Lawrence D Loomis-Price, Anna Loy, Carolina Lorusso, Dante Bassetti, Raffaele D'Amelio. (1998) Isoelectricfocusing and reverse blotting as a diagnostic tool in pediatric HIV infection. Journal of Clinical Virology 11:3, 203-210
   CrossRef

2. 2

   John L.K. Mokili, Jeffrey A. Connell, John V. Parry, Stephen D.R. Green, Antony G. Davies, William A.M. Cutting. (1996) How valuable are IgA and IgM anti-HIV tests for the diagnosis of mother-child transmission of HIV in an African setting?. Clinical and Diagnostic Virology 5:1, 3-12
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