- Unexpectedly low viral load : A minority of patients are long-term non-progressors, with persistently high CD4 cell counts. Another even more uncommon group are the “elite controllers" defined as having viral loads <50 c/mL without therapy for >1 year (Top HIV Med 2007;15:134). These patients are similar to patients with fully suppressive HAART in terms of HIV viral kinetics (CID 2008;47:102). Another group is "viremic controllers" defined by VL tests showing <2000 c/mL without therapy for >1 year. The frequency of elite controllers is estimated at 1 per 300 with HIV infection, undetectable VLs without treatment (J Exp Med 2006;203: 1357). There appears to be a genetic basis for this unusual degree of virologic control (Science 2007;317:944; Nat Genet 2007;39:733; Antivir Ther 2007; 27:406; JID 2008;197:563). It is usually associated with a sustained high CD4 count, but there are some notable exceptions that presumably reflect immune activation from other sources (CID 2008;46:e78).
- Subtype variations : The standard assays are most accurate for subtype B but are FDA-cleared for quantitation of subtypes A-G. A study of performance characteristics of non-subtype-B specimens found that the frequency of undetectable VLs or discordance by >1 log10 c/mL was 3% for Amplicor Monitor 1.5, 9% for Versant 3.0, and 15% for NucliSens (J Clin Microbiol 2005;43:3860). There is no commercially available quantitative test for HIV-2.
- Reservoirs : HIV resides in some anatomical sites that may be differentially affected by antiretroviral drugs and may be the source of archived strains resistant to these drugs. The most important and best characterized reservoirs are resting CD4 cells; others are cells in the CNS, GI tract (GALT) and genital tract (AIDS 2002;16:39; J Clin Microbiol 2000;38:1414; Ann Intern Med 2007;146:591; PNAS 2008;105: 3879; Ann Rev Med 2008;59:487).
RECOMMENDATIONS: Adapted from the International AIDS Society– USA (JAMA 2006;296:827) and Jan 29, 2008 DHHS Guidelines (www.aidsinfo. nih.gov/guidelines).Some of the commercially available tests are summarized and compared in Table 2-5.
- Quality assurance: Assays on individual patients should preferably be obtained at times of clinical stability, at least 4 weeks after immunizations or inter current infections, and with use of the same lab and same technology over time.
- Frequency and therapeutic monitoring: Tests should be performed at baseline and followed by routine testing at 3 to 4 month intervals (CID 2001;33:1060). With new therapy and changes in therapy, assays should be obtained at 1 to 4 weeks (alpha slope), at 12 to
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