Measurement of HIV RNA in patients infected by subtype C by assays optimized for subtype B results in an underestimation of the viral load

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Abstract
Quantitation assays of HIV‐1 RNA used currently were designed and optimized for subtype B viruses. However, infection with non‐B HIV viruses has become more common worldwide. Unfortunately, little information is available regarding the suitability of these assays for measurement of viral load in specific non‐B subtypes. The performance of two commercial HIV‐1 RNA quantitation assays was evaluated in 82 HIV subtype C‐infected patients and in 43 HIV‐1 subtype B‐infected patients. Blood samples were tested by the Amplicor HIV‐1 Monitor Assay, Version 1.5, and by the nucleic acid sequence‐based amplification HIV‐1 assay (NucliSens). The results were compared by using a paired, two‐tailed Student's t‐test; the difference between the assays was found to be significant only for subtype C. Discordant results (>0.5 log difference) between the two assays were detected in 39% of subtype C samples, compared to 23.2% of subtype B samples. In all cases in which a discordant result was detected, the lower results were obtained by the NucliSens assay. Discordant results between CD4 and viral load (CD4 < 200 cells/ml with a viral load <5,000 copies/ml) were observed in eight of the subtype C‐infected patients when a viral load was measured by NucliSens (9.7%), compared to three patients (3.6%) when measured by the Amplicor assay. In conclusion, in patients with HIV subtype C infection, measurement of HIV RNA by the NucliSens assay resulted in a significant underestimation of the viral load as compared to the Amplicor assay. As a consequence, such an underestimation may result in sub‐optimal care of patients infected with HIV subtype C. J. Med. Virol. 73:167–171, 2004.

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