HIV-1 RNA, Quantitative PCR

Clinical Use

•	Assess prognosis
•	Monitor progression of HIV-1 infection and determine when to initiate therapy
•	Monitor effect of antiretroviral drug therapy

Clinical Background
Measurement of HIV-1 RNA plasma levels (viral load) provides a direct assessment of viremia and should be used in conjunction with CD4+ T-cell counts. The baseline (pre-treatment) HIV-1 RNA level, combined with the baseline level of CD4+ T-cells, predicts progression to AIDS and death.^1,2

Periodic viral load assessment can be used to track the actual progression of the infection and is an essential parameter for determining when to initiate therapy. Once therapy has begun, HIV-1 RNA levels provide important information regarding therapeutic response.

Following initiation or a change in the antiviral regimen, responders show a rapid decline in viral load by 2 to 8 weeks and a maximum antiviral effect on HIV-1 RNA in 4 to 5 months.³ The goal is an approximate 1.0 log10 reduction within 2 to 8 weeks and a decline to below detectable levels (ultrasensitive PCR) by 16 to 24 weeks.³

In multiple studies, decreases in viral load have been correlated with improved clinical outcome (ie, survival). Such correlation was independent of pretreatment HIV-1 RNA levels, baseline CD4+ T-cells, and prior drug experience.

Thus, HIV-1 viral load measurement is essential for treatment optimization and should be used to assess therapeutic response and when making changes in therapy.

Measurement of the HIV-1 RNA level and the CD4+ T-cell count is recommended at the following times:

1. at the time of diagnosis;
2. every 3 to 4 months (HIV-1 RNA) or every 3 to 6 months (CD4+ T-cell count) to monitor progression in untreated patients;
3. on 2 occasions immediately prior to initiation of therapy;
4. 2 to 8 weeks and again at 3 to 4 months after initiation of therapy; and
5. every 3 to 4 months thereafter to monitor continuing effectiveness of therapy.³

If HIV-1 RNA is still detectable after 16 to 24 weeks of therapy, the measurement should be repeated for confirmation, using a second sample, prior to changing therapy.³ Do not perform HIV-1 RNA testing within 4 weeks of immunization or resolution of intercurrent infections.³

Individuals Suitable for Testing

•	Individuals recently diagnosed with HIV-1 infection
•	Individuals in the clinically latent period of the infection
•	Individuals undergoing antiretroviral therapy

Specimen Requirements
Centrifuge blood within 2 hours of collection and freeze without removing the plasma. Do not thaw.

Alternatively, submit EDTA (lavender-top tube) or ACD (yellow-top tube) frozen plasma that has been removed from cells and frozen within 2 hours of collection. Avoid repeated freezing and thawing. Note that specimens collected in ACD anticoagulant will have results that are 15% lower than those collected in EDTA owing to the dilution effect of the liquid anticoagulant.

Method

•	Reverse transcription of RNA, followed by polymerase chain reaction (PCR) amplification of cDNA
•	Hybridization of amplicons to HIV-1-specific capture probes
•	Colorimetric detection of HIV-1 cDNA
•	Reportable range for the standard quantitative, ultrasensitive, and expanded range assays, respectively: 400-750,000 copies/mL, 50-100,000 copies/mL, and 50-7,500,000 copies/mL4
•	Specificity: HIV-1 group M subtypes (clades) A through H; this Amplicor HIV-1 Monitor version 1.5 test provides a more accurate quantitation of non-B clades than previous versions.44
•	Synonyms: human immunodeficiency virus-1 (HIV-1) viral load
•	CPT Code*: 87536

Minimum Detectable Change in Viral Load⁴

Values obtained from different methods (eg, bDNA, PCR, NASBA) are not interchangeable due to variations in reagent specificity and other methodological differences. Use only one method when monitoring patients. If the methodology is changed, re-baselining is highly recommended prior to making clinical decisions.

Reference Range

Standard quantitative assay	<400 copies/mL
Ultrasensitive assay	<50 copies/mL
Expanded range assay	<50 copies/mL

Interpretive Information
Viral load data should be interpreted in the context of the patient's immunodeficiency status, among other factors. In general, therapy should be offered for asymptomatic individuals when the viral load is >55,000 HIV-1 RNA copies/mL (by bDNA or RT-PCR) or the CD4+ T cell count is <350 cells/mm.³ When the viral load is >55,000 copies/mL and the CD4+ T-cell count is >350/mm,⁴ some experts initiate antiretroviral therapy while others delay therapy and assess the CD4+ T-cell count more frequently. When the viral load is <55,000 copies/mL and the CD4+ T-cell count is >350/mm3, many experts defer therapy.

A 3-fold (0.5 log10) change in HIV-1 RNA viral load is considered clinically significant.³ Increasing levels may be due to disease progression, failed antiretroviral therapy, other active infections (eg, TB, pneumococcal pneumonia), or immunization. Decreasing levels indicate therapeutic response and improved outcome.

References

* The CPT code provided is based on AMA guidelines and is for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed.

Polymerase chain reaction (PCR) is performed pursuant to a license agreement with Roche Molecular Systems, Inc.

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