Pathology Associates Of Lexington, P.A.
Pathology Associates Of Lexington, P.A.
Pathology Associates Of Lexington, P.A.
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        Anti-HIV I (AIDS Virus) antibody
      
Rapid (and other) HIV test, blood

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 labs).

Maternal-fetal positivity

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 we agree).

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.

REFERENCES:

  1. Laboratory Medicine: Test Selection & Interpretation, Howanitz & Howanitz, 1991.

  2. The Reveal website

    [posted 2001; latest addition 30 December 2008]

 
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