This test is done in diagnostic situations via
our ER (and in other instances where persons are exposed to blood
of unknown status) for the rapid determination of negative
HIV-1 (HTLV-III) status. If the test result of this Reveal
(we used to use Abbott/Murex "SUDS" "Single Use
Diagnostic System" [taken off the market in 2000] for HIV-1...checks for antibody) test is
reactive, then the status of the person from whom the specimen
came is presumptively positive (the prior SUDS had to be considered
indeterminate), pending the formal lab tests (local EIA [for antibody]
followed by reference lab Western blot [highly specific antibody
tests directed toward purified viral core and envelope antigen
bands], if the EIA is reactive). In other words, a negative result
of the Reveal or the prior SUDS test is dependably negative; other
screening results of SUDS are reportedly undependable (although
our own experience has been that essentially all of SUDS "reactives" turn
out to be true Western blot positives), though a Reveal positive
is said to be a true positive in a high percentage of cases.
Positive rapid test results are reflexly followed
up locally with Abbott's EIA "beads" screening testing
(HIVABTMHIV-1/HIV-2 [rDNA] EIA).
Should the EIA results be indeterminate or positive (indeterminate
repeatedly on the original sample or on immediate new specimens),
the specimen is sent to a very high-quality virology reference
lab for clarifying or confirmatory testing by Western blot
analysis. If the final case disposition of that one specimen at
that one point in time is "indeterminate" even by Western
blot, then there is no choice but to let some time elapse and retest
on a new sample...the elapse in time will allow any confounding
agent in the patient to possibly be eliminated. Or, elapsed time
will allow the patient's system to more fully develop the agent
for a fully diagnostic test result.
Repeat reactive EIA plus indeterminate WB after 6 months in a low risk patient is a default "negative" HIV. While the same situation in a high risk patient remains indeterminate & needs continued monitoring.
If this indeterminate situation continues, one can
check for HIV-1 antigen by way of either a PCR-type of amplification test specific for either HIV-1 or HIV-2. Or
an EIA test for core p24 antigen (testing in specialty reference
A positive rapid screen in a mother delivering a
baby without prenatal testing, who additionally has the baby with
positive rapid test...both should be considered presumptively positive
until further results are final on the mother (the convention is
that baby is "positive" if mother is positive). Vaulting
straight to PCR testing on the baby may well be indicated.
Prenatal screening "problem"
In the Abbott EIA method of screening of prenatal specimens,
we (and Abbott reports that others have, too
) have encountered numerous examples of indeterminate or reactive
screens (interestingly, they are SUDS negative) which are Western
blot indeterminate or non-reactive. There is no choice but to recommend retesting
3-6 months later. Since we think that this non-negativity is
due to some pregnancy-associated biological false positive (BFP),
we have very little repeat testing data, the clinicians apparently
feeling comfortable that it is a biological false positive (and
Biological False Positives
Our QA/QC studies show that these prenatal
and other BFPs occur at a rate of about 0-0.5% of all EIA screening
tests and almost 50% of the reactive ones.
Laboratory Medicine: Test Selection & Interpretation,
Howanitz & Howanitz, 1991.
[posted 2001; latest addition 30 December 2008]