Viral-load testing

The viral load test quantifies viremia by measuring the amount of viral RNA. There are several methods used for determining the amount of HIV RNA reverse transcriptase-coupled polymerase chain reaction, branched DNA, and nucleic acid sequence-based assay. Each assay has its own lower limit of sensitivity, and results can vary from one assay method to the other therefore, it is recommended that the same assay method be used consistently within patients. 

Patients require close and regular (1- to 3-monthly) follow-up. The best indicator of antiretroviral activity is the HIV viral load, which should fall to below 20-50 copies per ml dependent on the detection limit of the viral load assay. However in most situations viral load testing is not feasible because of constraints on resources. 

The FDA approves an HIV viral load test Nevirapine, the first anti-HIV drug of the non-nucleoside reverse transcriptase inhibitors (NNRTl) Ritonavir Pi Indinavir Pis... 

Despite these intense efforts to test different chemical modifications, there is so far little success in developing potent and safe antivirals. For hepatitis C virus (HCV), McHutchison et al. reported in vivo side effects of a 20-nucleotide PS-modified ohgonucleotide (ISIS-14803) (McHutchison et al. 2006). In a test group of 28 patients, only 3 patients responded to the treatment by a reduction in the HCV viral load. The researchers concluded that further studies are needed to evaluate this novel agent and its side effects. Previously, ISIS Pharmaceuticals reported a 3.8 log reduction in plasma virus in patients with chronic HCV infection, using ISIS-14803 (www.isispharm.com). 

Currently, treatment of DSP and ATN is similar to many other neuropathies that have predominantly painful sensory involvement (Mendell and Sahenk 2003 Gonzalez-Duarte et al. 2007). It is purely symptomatic as there are no proven regenerative therapies to reverse the underlying process. An 8-month prospective pilot study reported an improvement in subjective quantitative sensory testing (QST) in HIV-infected patients who responded to HAART (Martin et al. 2000). The patients who did not respond to HAART did not show any improvements in QST. It is possible that suppression of viral load will slow the progression of DSP. Some studies have found a correlation between viral load and incidence (Childs et al. 1999), or severity (Simpson et al. 2002) of sensory neuropathy. Others, however, did not find any correlation between plasma viral loads and incidence of DSP or ATN (Brew et al. 2003). 

False-positive results with bDNA have been observed with proficiency testing specimens for HTV-1 in the College of American Pathologists HIV-1 viral load survey and HCV in the viral quality control program administered by the Netherlands Red Cross. The reason for the false-positive results with these proficiency testing specimens is not known but may be sample matrix effects. The extent to which this problem occurs with clinical samples has not been determined. However, both the HIV-1 and HCV bDNA assays were designed to have a false-positive rate of 5%. 

In 1996, after eight years in the planning stage, a quantitative PCR assay for HIV-1 in human plasma was released by Roche Molecular Systems. This test, the result of intensive efforts by John Sninsky and his team at Roche, allowed quantitation of HIV-1 viral load to 400 viral copies (just 200 viral particles, as each HIV-1 virion contains two copies of the virus). 

B16. Boulet, P., Barjon, P., Crastes de Paulet, A., and Floch, H., The L-tiyptophan loading test in viral hepatitis. Rev. Franc. Ftudes Clin. Biol. 7, 857-861 (1962) Chem. Abstr. 58, 8313 (1963). 

In vitro tests have shown that valproate can increase the viral burden in HIV-infected individuals by potentiating replication of the virus (110). In a retrospective review of 11 HIV-positive patients with behavioral disturbances taking valproate HIV-1 viral load did not increase in six of the nine patients who had measurements between the first week and 3.5 months after the start of valproate treatment no follow-up was available for the other three (111). These data suggest that, contrary to in vitro data, HIV-1 viral load is not adversely affected by valproate in the presence of effective antiretroviral therapy. 

Taken together, PERT assays can be used to detect and quantitate retroviruses. The advantages compared with amplification procedures for specific viral sequences are obvious one test fits all existing retroviruses, and there is no impediment to sensitivity owing to sequence variation, which is a documented drawback of viral load measurements by PCR (16). 

Laboratories should process specimens in a class 11 biological safety cabinet using level 3 practices. When possible, staff should pretreat serum with a combination of heat-inactivation at 56°C and polyethylene glycol p-tert-octylphenyl ether (Triton X-1(X)). Although treatment with lOuL of 10% Triton X-100 per 1 mL of serum for an hour reduces the virus titer in the serum, laboratory staff should not assume that the resulting viral titer is zero. For laboratory tests in which detergent use could alter the results, heat inactivation alone may help reduce the viral load and consequent infectivity of the sample. 

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