Efficiency of drug resistance genotypic tests in specimens with low HIV viral load

The early recognition of resistance to antiretroviral agents could allow a rapid switch in therapy and therefore avoid the accumulation of mutations and reduce the risk of cross-resistance. However, the efficiency of genotypic tests in specimens with low viral load (VL) is severely compromised since human immunodeficiency virus (HIV) RNA in these samples often goes unrecognized. The frequency of results provided by a line probe assay (LiPA, Murex), a commercially available drug resistance test and a home-made point mutation assay (PMA) for recognizing the codon 151 multidrug-resistance mutation was examined in 664 plasma samples stratified with respect to VL values. Overall, 421 (63%) samples could be interpreted by both LiPA and PMA. The sensitivity decreased as plasma VL lowered: 89% for samples with VL > 10,000 HIV RNA copies/ml, 77% for those with VL between 500 and 10,000 HIV RNA copies/ml and 37% for specimens with VL < 500 HIV RNA copies/ml. A good agreement existed comparing the sensitivity of the home-made PMA and LiPA. Although the former tends to produce more results, the difference did not achieve statistical significance. Our results support that new, more sensitive, HIV RNA extraction methods need to be implemented for the rapid recognition of drug-resistant mutants in patients experiencing an early rebound in plasma viraemia.