Recombigen HIV-1 Latex Agglutination (LA) Test (8/1/89)

Date:      August 1, 1989
 
From:      Director, Center for Biologics Evaluation and Research

Subject:   Use of the Recombigen HIV-1 Latex Agglutination (LA)
           Test

To:        All Registered Blood and Plasma Establishments

On February 1, 1989 this office issued a memorandum regarding the
use of the Recombigen HIV-1 LA test in blood and plasma
establishments. This memorandum is intended to clarify certain
statements in the February 1 memorandum. In addition, this
memorandum addresses FDA recommendations concerning the use of
rapid tests for "pre-collection screening."

1.   Clarifications to the memorandum of February 1, 1989

     Our February 1 memorandum stated that the latex
     agglutination test is not recommended for routine use
     in blood and plasma establishments because of
     procedural difficulties in testing large numbers of
     donor samples. This recommendation has been
     misinterpreted to mean that the test is not suitable
     for any use in blood and plasma establishments. As
     previously stated, the latex agglutination test may
     be used, with the exercise of medical discretion, in
     situations in which screening by EIA is impractical
     or unavailable. For example, in emergency situations,
     the latex test could be used to screen whole or rare
     blood donors. It might also be used for testing
     previously-screened platelet donors. Results from a
     latex screen will determine the HIV-1 status of the
     donor; repeatably reactive donors must be deferred,
     although they remain eligible for reentry.

     The prior memorandum mentioned circumstances which
     could  give rise to false positive results. This test
     requires subjective reading and interpretation,
     necessitating proper  training of personnel to insure
     correct results. Because  blood bank technicians may
     not have occasion to use the test on a regular basis,
     the interpretation panel should be used periodically,
     as recommended in the package insert. Clinical trials
     performed in blood banks by properly trained
     operators showed the latex test to be 99.5% specific.

2.   Use of rapid screening tests for "pre-collection
     screening"  Following the licensure of a rapid
     screening test for  antibodies to HIV-1, this office
     received inquiries about the possibility of screening
     donors of blood or plasma prior to collection. Such a
     practice might be useful to avoid  performing lengthy
     and expensive apheresis procedures on donors whose
     donations would be subsequently discarded. Tests used
     to determine donor suitability may be performed 
     prior to the collection, but on the same day (21CFR 
     640.3(a)). If an HIV-1 antibody test is performed in
     the "pre-collection screening" mode, it would become
     improper to draw a unit from a person with a
     repeatably reactive result.

     Tests performed "pre-collection" do not obviate the
     performance of required tests at the time of
     collection on the unit or on the donor (2lCFR
     640.4(g)(2), and 2lCFR 640.5). If a situation should
     occur in which another licensed test for HIV-1
     antibodies is performed and found to be repeatedly
     reactive on a unit from a donor who tested negative
     in a "pre-collection screen," the unit should be
     discarded and the donor deferred despite the negative
     result of the pre-collection test.

The Medical Director, in using tests in the circumstances
outlined above, should pay special attention to the potential for
difficulties in maintaining confidentiality and of inadvertent de
facto donor notification in the absence of additional testing for
specificity.

                                 Paul D. Parkman, M.D.
                                 Director
                                 Center for Biologics
                                   Evaluation and Research