1. LABORATORY SUPPORT IN
MANAGEMENT AND
TREATMENT OF HIV
INFECTION
Dr Abhijit Chaudhury MD,DNB,
Diplomate of American Board.
Professor, Dept of Microbiology.

2. Importance Of Laboratory in
Management of HIV Infection
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DIAGNOSIS
ASSESS THE NEED FOR THERAPY
ASSESS THE EFFECTIVENESS OF
ART
HELP IN DECISION MAKING FOR
CHANGE OF THERAPY (Treatment
Failure)
DRUG TOXICITY MONITORING
(BIOCHEMISTRY)

3. Basic Tools
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Nucleic Acid Testing (NAT).
CD4+ Lymphocyte Count.
Phenotype Testing for Drug Resistance.

4. NAT
NAT is the detection of DNA/RNA in
patient’s sample.
PCR : Useful for detection and identification
of a wide variety of organisms in patient’s
samples. Highly specific and sensitive.
Even a few organisms present can be
detected.

5. Polymerase Chain Reaction
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Amplification technique.
A huge number of copies of DNA/ RNA
can be made from a single copy.
30-40 cycles will generate ~ 1 million
copies.
Results are available in 24-48 hrs.

6. Basic Steps of PCR
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Denaturation: The double stranded DNA is
melted to open the single strands at 94 C.
Annealing( 54 C) Primer is added( Small piece
of DNA of a particular organism) which binds
with portions of the sample DNA ( Template)
and starts copying the template.
Extension ( 72 C): Under the influence of the
added Taq polymease enzyme both strands of
the DNA get copied. One DNA becomes 2!

10. NAT
Commercially 4 types of test formats are
available for HIV:
1. PCR to Detect Proviral DNA
2. RT-PCR: PCR amplification of cDNA generated
from viral RNA ( Target amplification). Can
detect up to 40 copies/ml of RNA.
3. bDNA Assay: Nucleic acid capture assay using
signal amplification. Isothermic process. Reliable
to 75 copies/ml
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11. NAT
4. NASBA ( Nucleic acid sequence based assay) :
Isothermic nucleic acid amplification with internal
controls. Can detect minimum of 176 copies/ml
of RNA.
5.Product Enhanced RT (PERT) Assay (Not
available commercially). 106 -107
times more sensitive than RT-PCR, can detect 10
viral particles.

12. NAT-Importance
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Used for definitive diagnosis of HIV
infection in infants and children aged
under 18 months. No role in diagnosis in
adults
Used for virus quantification
Used for drug resistance testing
No commercial NAT kit is available for
detection or quantification of HIV 2.

13. CD4+ T- Lymphocyte Count.
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The Gold Standard of CD4 cell count is
the Flow Cytometry Method using
Fluorescent Activated Cell Sorter.
The absolute count in Indian population
varies from ~ 700-900/cu mm.

16. CD4+ Lymphocyte Count
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The major indicator of immune function
Most recent CD4 count is best predictor of
disease progression
CD4 count usually is the important consideration
in decision to start ART
Important in determining response to ART
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Adequate response: CD4 increase 100-150 cells/µL per year
CD4 monitoring
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Check at baseline (x2) and at least every
3-6 months

17. CD4+ Lymphocyte Count
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Exact CD4 count at which to initiate therapy
not known, but evidence points to starting at
higher counts
Current recommendation: ART for all patients
with CD4 counts of <350 cells/µL, certain
others regardless of count.

18. Indications for Initiating ART:
Chronic Infection
Clinical Category and/or
CD4 Count
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History of AIDS-defining illness
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CD4 count of <350 cells/µL
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Pregnant women
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HIV-associated nephropathy
Recommendation
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Hepatitis B coinfection, when
HBV treatment is indicated
Initiate ART

19. Indications for Initiating ART:
Chronic Infection
Clinical Category and/or
CD4 Count
CD4
count of >350 cells/µL,
asymptomatic, without
conditions listed above
Recommendation
Optimal time to initiate ART is
not well defined; consider
individual patient characteristics
and comorbidities

20. VIRAL LOAD
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HIV RNA
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Less important than CD4 count, but may influence decision to
start ART and help determine frequency of CD4 monitoring
> 50,000 copies of RNA/ml is an indication for initiation of ART.
Critical in determining response to ART
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Goal of ART: HIV RNA below limit of detection (ie, <40 to <80
copies/mL, depending on assay)
RNA monitoring
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Check at baseline (x2)
Immediately before initiating ART
2-8 weeks after start or change of ART (Normal response is
tenfold decrease in HIV RNA level within 4-8 weeks)
Every 3-4 months with stable patients

21. Treatment Failure
A. VIROLOGIC FAILURE
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Incomplete virologic response:
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In patient on initial ART, HIV RNA >400
copies/mL after 24 weeks on therapy or >50
copies/mL by
48 weeks (confirm with second test)
Virologic rebound:
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Repeated detection of HIV RNA
after virologic suppression
(eg, >50 copies/mL)

22. Treatment Failure
B. IMMUNOLOGIC FAILURE
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Failure to achieve and maintain adequate CD4
response despite virologic suppression
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There is no specific definition for immunologic failure, although
some studies have focused on patients who fail to increase CD4
T-cell counts above a specific threshold (e.g. >350 or 500
cells/mm3) over a specific period of time (e.g. 4–7 years).
Persistently low CD4 count while on suppressive
ART is associated with increased risk for
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AIDS-related complications

23. Resistance Testing
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Before initiation of ART:
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Resistance testing (genotype) recommended for all at entry to care
Recommended for all pregnant women
Transmitted resistance in 6-16% of HIV-infected patients
Identification of resistance mutations may optimize treatment outcomes
In absence of therapy, resistance mutations may decline
over time and become undetectable by current assays, but
may persist and cause treatment failure when ART is started
Patients with virologic failure:
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Perform while patient is taking ART, or ≤4 weeks after
discontinuing therapy
Interpret in combination with history of ARV exposure
and ARV adherence

24. Resistance Testing- GENOTYPING
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Detects drug resistance mutations in
specific genes
(eg, reverse transcriptase and protease)
Sequencing or probing
Results within 1-2 weeks
Interpretation of mutations and crossresistance is complex
Consultation with specialists is
recommended

25. Resistance TestingPHENOTYPING
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Measures the ability of viruses to grow in various
concentrations of ARV drugs
Results within 2-3 weeks
More expensive than genotyping
The ratio of the IC50s of the test and reference
viruses is reported as the fold increase in IC50,
or fold resistance
Interpretation may be complex
Consultation with specialists is recommended

26. Coreceptor Tropism Assay
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Should be performed when CCR5
antagonist is being considered
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Maraviroc should be given only to patients
with exclusive CCR5 tropism
Current commercially available tropism assay
is 100% sensitive for CXCR5 clones that
make up ≥0.3% of the population
Consider in patients with virologic failure
on a CCR5 antagonist.

27. List Of Lab Tests at Initiation of
Therapy
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BASELINE EVALUATION:
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HIV antibody
CD4 cell count
Plasma HIV RNA
Resistance test (genotype)
CBC, chemistry profile, BUN, Cr, transaminase
Fasting glucose and lipids
RPR or VDRL
Hepatitis A, B, C serology
Toxoplasma IgG

28. List Of Lab Tests at Initiation of
Therapy: Additional Tests
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Tuberculin skin test (TST) or IFN-γ release
assay
Chest X ray (if symptoms, or positive
Tuberculin test or IFN-γ release assay)
Gynecologic exam with Pap smear
Testing for Chlamydia and gonorrhoea

29. WHO Recommendations for
Resource Limited Settings
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In the absence of a CD4 cell count, a total lymphocyte
count (TLC) below 1200 cells/mm3 in patients with
symptomatic HIV disease has been recommended as a
guide to the initiation of ART.
Data suggest that a TLC below 1200 cells/mm3 as a
surrogate for a CD4 count below 200 cells/mm3 has high
positive predictive value but poor negative predictive
value and that it cannot be used alone in asymptomatic
patients to determine treatment eligibility.
WHO considers that TLC should be gradually eliminated
from the adult ARV guidelines.

33. Conclusion
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Laboratory support is absolutely essential in the
management of HIV infected patient.
There is an urgent need to establish an HIV
laboratory at SVIMS with the minimum
capabilities as recommended by WHO
( Diagnostic, CD4 count, Viral load estimation).
THE END