Page 62 - AIDSBK23C

Page 62

level of reactivity gives an indication of predictive value of an EIA test—the more reactive the
test, the more likely the test result is a true positive.[341]
Tests for confirmation of a reactive EIA include Western blot (WB), line immunoassay
(LIA), indirect immunofluorescence assay (IFA), HIV-1 RNA assay, or additional EIA testing.
When funding for routine laboratory confirmatory tests is available, WB, LIA, IFA, or HIV-1
RNA can be done, and the most commonly employed test is WB. Detection and confirmation of
acute HIV infection as quickly as possible would require use of a sensitive EIA for HIV
antigen/antibody, followed by HIV-2 testing, followed by HIV-1 RNA assay on the HIV-1
antigen positive specimens. When rapid and simple testing is required, then algorithms for use
of EIAs include: (1) a standard EIA followed by a rapid EIA, (2) two standard EIAs, or (3) two
rapid EIAs. EIA tests can be utilized which have reactivity to different HIV antigens from
different sources or using different methodologies.[333,335]
In a population with a low prevalence for HIV-1 (no risk factors), about 6 or 7 positive
EIA test results per million tests performed will be false positives. False positive EIA results
may occur in persons with hematologic malignancies, acute DNA viral infections, serum
autoantibodies, autoimmune diseases, alcoholic hepatitis, renal failure, cystic fibrosis, multiple
pregnancies or blood transfusions, hemodialysis, anti-HLA-DR4 antibodies, and vaccinations for
hepatitis B, rabies, or influenza. Positive specimens should be repeatedly positive, with
confirmation by an additional laboratory test, before reporting them as such. Positive EIA tests
are confirmed by the more specific, but expensive and difficult to perform, Western blot
test.[329,342]
False negative results can occur, and the EIA method will also miss recently infected
persons in the "window" of time prior to seroconversion, which can be as little as a week, but up
to 3 weeks, on average. EIA is of no value to detect infected infants of HIV-1 positive mothers
since transplacentally acquired maternal antibody may persist up to 15 months postpartum.
Though a very rare occurrence, not all HIV-1 infected persons have detectable antibody during
all or part of their course because of delayed seroconversion.[196] Explanations for
seronegativity include: marked hypogammaglobulinemia, B cell functional defects,
chemotherapy, a non-detectable subgroup of HIV, or a laboratory error. In those patients with
persistently decreased CD4 counts, the possibility of idiopathic CD4+ T-lymphocytopenia (ICL)
may be considered. When there is evidence suggesting HIV infection but a negative EIA, then
tests for p24 antigen, HIV-1 RNA, and/or viral culture can be considered.[343] There is no
evidence for seroreversion, or loss of detectable antibody to HIV-1 once true seroconversion
occurs.[199]
Dried blood or plasma spots on paper can be utilized to collect, store, and ship patient
samples for HIV-1 RNA viral load testing or genotyping, particularly in places where resources

are limited. One limitation is the small amountof blood in a dried spot, which may results in

reduced sensitivity in detectingHIV-1 RNA when the viral burden is below 1000 to 4000
copies/mL. The spots have been stored for up to a year at room temperature without significant
loss of HIV-1 RNA.[344]
Home-based testing kits utilizing EIA methodology have been marketed. Blood
specimens are collected via fingerstick. When properly collected, the accuracy is similar to that
of standard serum EIA testing collected by health care workers. However, specimens may not be
properly collected. Counseling regarding test results may not be sought. When combined with
counseling, the use of home testing for HIV can be an effective alternative to standard testing
offered in the health care setting.[345] However, if home testing is mainly utilized by low risk