Biomedical Engineering Reference
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is vital to determine when to initiate antiretroviral therapy and when to initiate
prophylaxis against opportunistic infections. The Centers for Disease Control 1993
Revised Classification System for HIV infection emphasizes the clinical importance
of the CD4 T cell count in the categorization of HIV-related clinical conditions [13].
Although ARV therapy and prophylactic therapies for different types of OIs increase
survival rate and decrease the risk of developing coinfections in HIV-infected
patients, they can be toxic, invasive, and expensive; therefore, it is important to
evaluate the risk of progression to AIDS and developing OIs using CD4 counts to
avoid giving unnecessary treatment.
Normal CD4 levels for adults are around 1000 cells/
m
L, but can range from 450 to
over 1500 cells/
L (Table 8.2) [29, 30]. As stated previously, the clinical definition of
AIDS is having CD4 levels at less than 200 cells/
m
L [12, 13]. At this point, the risk of
developing opportunistic infections increases. Prophylaxis against opportunistic
infections should be started at various CD4 counts depending on the type of infection.
The three most common AIDS-related opportunistic infections associated with
increased mortality include Pneumocystis carinii pneumonia, cytomegalovirus, and
Mycobacterium avium complex [14]. Primary prophylaxis for Pneumocystis carinii
pneumonia should be started at a CD4 count of
m
L or if there is a history of
oropharyngeal Candida, and prophylaxis should be discontinued if the CD4 count
stays greater than 200 cells/
200 cells/
m
<
L for at least 3 months [31, 32]. For toxoplasmosis,
criteria for starting primary prophylaxis include the presence of immunoglobulin G
(IgG) antibody to Toxoplasma and a CD4 count of
m
m
<
100 cells/
L [31]. Treatment
may be discontinued with a CD4 count greater than
L for at least
3 months [31, 32]. Primary prophylaxis against disseminated Mycobacterium avium
complex should be started with a CD4 count
200 cells/
m
<
50 cells/
m
L and can be stopped if the
<
CD4 count stays greater than
L for at least 3 months [31, 32]. For
relatively rare OIs such as Cryptococcosis, Histoplasmosis, and Cytomegalovirus
Retinitis, routine testing in asymptomatic individuals is recommended only for
patients living in regions where these OIs are endemic. Antifungal prophylactic
therapy is not usually recommended because of the lack of demonstrated survival
benefits and the possibility of drug interactions, drug resistance, and cost [32].
Highly active antiretroviral therapy (HAART) works by suppressing viral
replication, which allows CD4 T cells to reconstitute. There is no universal or
global consensus as to when to initiate antiretroviral therapy. Reference ranges on
the initiation of ARV and prophylaxis against OIs vary from more developed
countries to less developed countries based on disease prevalence, financial
burden, and the capacity and infrastructure of the health systems [2]. The U.S.
Health and Human Services recommends starting ARV when counts are
100 cells/
m
<
200
<
cells/
L, patient comorbidities and individual
scenarios should be taken into account before starting ARV [33]. ARV should also
be initiated in pregnant women, those having a history of AIDS-defining illness,
persons with HIV-associated nephropathy, and in individuals coinfected with the
Hepatitis B virus (HBV) (Table 8.3) [33]. The World Health Organization (WHO)
recommends that ARV be considered at CD4 counts
m
L and when counts are
350 cells/
m
<
m
<
350 cells/
LandthatARV
m
should be initiated in all patients who have CD4 counts
L. Where CD4
testing is unavailable, the WHO clinical staging criteria can be used (Table 8.4). It
<
200 cells/
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