HIV-1 RNA Quantification, Plasma
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Currently, there are 2 types of HIV, HIV type 1 (HIV-1) and HIV type 2 (HIV-2). HIV-1 has been isolated from patients with AIDS, AIDS-related complex, and asymptomatic infected individuals at high-risk for AIDS. Accounting for >99% of HIV infection in the world, HIV-1 is transmitted by sexual contact, by exposure to infected blood or blood products, from an infected pregnant woman to fetus in utero or during birth, or from an infected mother to infant via breast-feeding. HIV-2 has been isolated from infected patients in West Africa and it appears to be endemic only in that region. However, HIV-2 also has been identified in individuals who have lived in West Africa or had sexual relations with individuals from that geographic region. HIV-2 is similar to HIV-1 in its morphology, overall genomic structure, and ability to cause AIDS.
Multiple clinical studies of plasma HIV-1 viral load (expressed as HIV-1 RNA copies/mL of plasma) have shown a clear relationship of HIV-1 RNA copy number to stage of HIV-1 disease and efficacy of anti-HIV-1 therapy. Quantitative HIV-1 RNA level in plasma (ie, HIV-1 viral load) is an important surrogate marker in assessing the risk of disease progression and monitoring response to anti-HIV-1 drug therapy in the routine medical care of HIV-1-infected patients.
HIV serologic tests may be unreliable for infants born to HIV-infected mothers. In infants up to 18 months of age, positive serologic test results can be due to the presence of maternal HIV antibodies. Therefore, the United States Working Group on Antiretroviral Therapy and Medical Management of HIV-Infected Children recommends use of proviral DNA or RNA tests for the detection of HIV infection in infants born to HIV-infected mothers.(3)
Quantifying plasma HIV-1 RNA levels (viral load) in HIV-1-infected patients:
-Before initiating anti-HIV-1 drug therapy (baseline viral load)
-Who may have developed HIV-1 drug resistance while on anti-HIV-1 therapy
-Who may be noncompliant with anti-HIV-1 drug therapy
Monitoring HIV-1 disease progression while on or off anti-HIV-1 drug therapy
Evaluating infants <18 months of age born to HIV-infected mothers
This assay has a plasma HIV-1 RNA quantification result range of 20 to 10,000,000 copies/mL (1.30-7.00 log copies/mL).
An "Undetected" result indicates that the assay was unable to detect HIV-1 RNA within the plasma specimen.
A "Detected" result with the comment, "HIV-1 RNA level is <20 copies/mL (<1.30 log copies/mL). This assay cannot accurately quantify HIV-1 RNA below this level" indicates that HIV-1 RNA is detected, but the level present is less than the lower quantification limit of this assay.
A "Detected" result with the comment, "HIV-1 RNA level is >10,000,000 copies/mL (>7.00 log copies/mL). This assay cannot accurately quantify HIV-1 RNA above this level" indicates that HIV-1 RNA is detected, but the level present is above the upper quantification limit of this assay. Due to the increased sensitivity of this assay, patients with previously low or undetectable HIV-1 viral load may show increased or detectable viral load with this assay. However, the clinical implications of a viral load below 20 copies/mL remain unclear. Possible causes of such a result include very low plasma HIV-1 viral load present (eg, in the range of 1-19 copies/mL), very early HIV-1 infection (ie, less than 3 weeks from time of infection), or absence of HIV-1 infection (ie, false positive).
For the purpose of patient monitoring, the United States Department of Health and Human Services Panel on Antiretroviral Guidelines for Adults and Adolescents defines virologic failure as a confirmed viral load of >200 copies/mL, which eliminates most cases of viremia resulting from isolated blips or assay variability. Confirmed viral load rebound (ie, >200 copies/mL) on 2 separate tests obtained at least 2 to 4 weeks apart should prompt a careful evaluation of patient's tolerance of current drug therapy, drug-drug interactions, and patient adherence.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
This test is not licensed by the FDA as a screening test for HIV-1 infections in a post-exposure setting. Although this quantitative HIV-1 RNA test is not FDA-approved for diagnostic purposes, the United States Working Group on Antiretroviral Therapy and Medical Management of HIV-Infected Children recommends the use of molecular-based assays to detect HIV-1 RNA or proviral DNA for the diagnosis of HIV infection in infants of <18 months of age and born to HIV-infected mothers.
A single HIV-1 viral load test result should not be used as the sole criterion in guiding therapeutic decisions and intervention in the clinical care of HIV-1-infected patients. Viral load results should be correlated with patient symptoms, clinical presentation, and CD4 cell count. Due to the inherent variability in the assay, physiologic variation and concurrent illnesses in the infected patients, <100-fold (<2 log) changes in plasma HIV-1 viral load should not be considered to be significant changes.
Viral load results of <20 copies/mL do not necessarily indicate absence of HIV-1 viral replication. Inhibitory substances may be present in the plasma specimen, leading to negative or falsely low HIV-1 RNA results. Improper specimen collection or storage may lead to negative or falsely lower plasma viral load results.
Although this commercial HIV-1 viral load assay is optimized for quantification of plasma viral load in HIV-1 infection due to HIV-1 groups M (subtypes A to H) and O strains, results generated from HIV-1 group O strains may be discordant (> or =0.5 log copies/mL) with those obtained from other commercially available HIV-1 viral load assays. The assay is not reliable for quantifying plasma viral loads in infection caused by HIV-1 group N and HIV-2 strains.
ACD-plasma specimens are not optimal for HIV-1 viral load testing because such plasma specimens show quantitative HIV-1 RNA levels that are approximately 15% lower than those collected in tubes containing EDTA.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Relucio K, Holodniy M: HIV-1 RNA and viral load. Clin Lab Med 2002;22:593-610
2. Thompson MA, Aberg JA, Cahn P, et al: Antiretroviral treatment of adult HIV infection: 2010 recommendations of the International AIDS Society-USA panel. JAMA 2010;304:321-333
3. Panel on Antiretroviral Guidelines for Adults and Adolescents. Guidelines for the use of antiretroviral agents in HIV-1-infected adults and adolescents. Department of Health and Human Services. January 10, 2011;1-166. Available from URL: http://www.aidsinfo.nih.gov/ContentFiles/AdultandAdolescentGL.pdf