Evaluation of two commercially available, inexpensive alternative assays used for assessing viral load in a cohort of human immunodeficiency virus type 1 subtype C-infected patients from South Africa

Abstract

Although human immunodeficiency virus type 1 (HIV-1) RNA is the acknowledged "gold standard" marker for monitoring disease activity in patients receiving highly active antiretroviral therapy (HAART), it remains unaffordable in resource-constrained settings. The present study investigated two commercially available kits for the detection of HIV-1 viral load markers as more affordable alternatives to HIV-1 RNA quantitation. The greatly improved heat-denatured, signal-boosted HiSens HIV-1 p24 Ag Ultra kit (Perkin-Elmer) and the ExaVir Load Quantitative HIV-RT kit (Cavidi Tech AB) were compared with the Amplicor HIV-1 Monitor (version 1.5) assay (Roche Molecular Systems Inc.). A total of 117 samples containing HIV-1 subtype C were analyzed by all three methodologies. Eighty-nine of these samples represented serial measurements from 20 patients receiving HAART. The remaining samples analyzed were from a group of treatment-naive patients. The association between the p24 antigen assay and the RNA assay was fairly strong (R(2) = 0.686). The association between the reverse transcriptase (RT) quantitation assay and the RNA assay was strong (R(2) = 0.810). Both alternative assays seemed most useful for the serial monitoring of patients receiving HAART (n = 89 plasma samples from 20 patients), as all assays showed a statistically significant downward trend over time, with the trend being either linear or curvilinear. In addition, all three assays showed negative correlations with the CD4 count (CD4 count versus RNA load, r = -0.336 and P = 0.001; CD4 count versus p24 antigen level, r = -0.541 and P < 0.0001; CD4 count versus RT level, r = -0.358 and P = 0.0006). Still of major concern are both the lack of sensitivity and the wide degrees of variability of both assays. However, both assays provide a less expensive alternative to the Roche viral load assay and demonstrate the same trends during treatment.

FIG. 1.

(a) Distribution of log₁₀ RNA results. Of the samples tested (n = 117), 40.5% had viral loads <2.8 log₁₀ (630 copies/ml). (b) Range of CD4 counts in 20 patients over six visits (n = 89).

FIG. 2.

Scatterplots of log₁₀ p24 antigen level versus log₁₀ RNA load (a) and log₁₀ RT level versus log₁₀ RNA level (b) (n = 117 samples).

FIG. 3.

(a) Schematic box plots showing log₁₀ p24 antigen and log₁₀ RNA levels. Darker boxes, p24 antigen levels; lighter boxes, RNA load. (b) Schematic box plots showing log₁₀ RT level and log₁₀ RNA levels. Darker boxes, RT levels; lighter boxes, RNA level. The secondary axis versus the six visits over time was used (n = 89 samples). A line has been drawn through the median of each visit.