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phase of infection, and finally increased viremia with progression to clinical AIDS. The HIV-1
RNA correlates with plasma viremia and the level of p24 antigen, but is more sensitive, and can
predict HIV disease progression independently of CD4 lymphocyte counts. This assay also has
usefulness for closely monitoring patient response to antiretroviral therapy. An early response to
therapy is marked by a decrease in viremia, while increasing drug resistance is indicated by
increasing viremia.[370,371,372]
However, just as with CD4 lymphocyte counts, there can be variability in bDNA assays
of HIV-1 RNA. Though there is no diurnal variation, the HIV-1 RNA level may have up to a 0.4
log variance. Genetic subtypes of HIV-1 may provide differences up to a factor of 1.5. The
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plasma levels of HIV-1 RNA have been shown to increase transiently during bacterial infections.
There is lack of standardization among different methodologies. Thus, testing for HIV-1 RNA is
not routinely used for diagnosis of HIV-1 infection.[373,374]
A qualitative HIV-1 RNA test on plasma is available for use in the initial diagnosis of
HIV infection. Detectable HIV-1 RNA may appear less than 2 weeks following infection.
Quantitative HIV-1 RNA tests with sensitivity of 50 copies/mL can detect HIV infection before
both the p24 antigen test and EIA tests, but RNA NAAT testing has been limited primarily to
quantifying HIV-1 loads and screening blood donations because the tests are expensive and
technically complex to perform. Moreover, low-positive HIV RNA levels (<5,000 copies/mL)
may represent a false-positive test result, but HIV-1 RNA levels during acute HIV infection are
usually quite high (>100,000 copies/mL).[332] Qualitative HIV-1 RNA testing has been applied
as a confirmatory test for EIA positive specimens.[375]

HIV-1 REVERSE TRANSCRIPTASE ASSAY.-- An alternative to measuring HIV-1
RNA viral load is the measurement of viral reverse transcriptase (RT). The equipment and
technology for this alternative RT assay are simpler and less expensive than those for standard
viral load testing. The RT assay compares comparably with viral load testing, but not
genotyping.[376]

NUCLEIC ACID TESTING.—NAT, or nucleic acid amplification testing (NAAT) is
based upon the amplification of HIV RNA in plasma. It is possible for this test to detect the
presence of HIV RNA up to 11 to 12 days prior to ELISA and 3 to 6 day before the p24 antigen
is detected. Thus, NAT has been utilized as a means for reducing the "window" period to only
10 to 12 days from HIV infection to serologic positivity for screening blood product donations.
Such tests can potentially detect levels of HIV RNA as low as 5 to 40 copies/mL.[377,378]

IMMUNOHISTOCHEMISTRY.-- Immunohistochemical staining methods for diagnosis
of HIV-1 in tissues make use of a monoclonal antibody raised against HIV-1 antigen. This is
used to detect cells containing HIV-1 provirus in 10% (v/v) neutral buffered formalin-fixed,
paraffin-embedded tissues. The method is similar to other immunohistochemical staining
methods and can be employed by many laboratories that already use this technique. However, it
is not as sensitive as methods that employ DNA probes. Immunohistochemical reagents with
antibody to the p24 can identify HIV infection involving follicular dendritic cells in lymphoid
tissues. Additional cells that may be positive with p24 antigen include intrafollicular
lymphocytes, small mantle zone lymphocytes, paracortical small and large lymphocytes,
macrophages and multinucleated giant cells. Peripheral blood mononuclear cells and
multinucleated giant cells may also be positive. Immunohistochemical identification may be