Monitoring Virologic Responses to Antiretroviral Therapy in HIV-Infected Adults in Kenya: Evaluation of a Low-Cost Viral Load Assay

A key advantage of monitoring HIV viral load (VL) in persons receiving antiretroviral therapy (ART) is the ability to detect virologic failure before clinical deterioration or resistance occurs. Detection of virologic failure will help clarify the need for enhanced adherence counseling or a change to second- line therapy. Low-cost, locally performable alternates to expensive VL assays are needed where resources are limited.We monitored the response to 48-week ART in 100 treatment-naïve Kenyan adults using a low-cost VL measurement, the Cavidi reverse transcriptase (RT) assay and gold-standard assays, Roche RNA PCR and Bayer Versant HIV-1 RNA (bDNA) assays. In Altman-Bland plots, the mean difference in viral loads between the three assays was small (<0.5 log(10) copies/mL). However, the limits of agreement between the methods exceeded the biologically relevant change of 0.5 log copies/ml. Therefore, the RT assay cannot be used interchangeably with the other assays to monitor individual patients. The RT assay was 100% sensitive in detecting viral loads of > or =400 copies/ml compared to gold-standard assays. After 24 weeks of treatment, viral load measured by the RT assay was undetectable in 95% of 65 patients with undetectable RNA PCR VL (<400 copies/ml), 90% of 67 patients with undetectable bDNA VL, and 96% of 57 patients with undetectable VL in both RNA PCR and bDNA assays. The negative predictive value of the RT assay was 100% compared to either assay; the positive predictive value was 86% compared to RNA PCR and 70% compared to bDNA.The RT assay compared well with gold standard assays. Our study highlights the importance of not interchanging viral load assays when monitoring an individual patient. Furthermore, the RT assay may be limited by low positive predictive values when used in populations with low prevalence of virologic failure

Characteristics associated with HIV RNA PCR virologic failure for antiretroviral naïve patients receiving antiretroviral therapy (ART), Mombasa, Kenya.^a

a<p>Excludes patients who died, were lost to follow up or transferred care to another institution.</p>b<p>OR, Odds Ratio; CI, Confidence interval.</p>c<p>By Student's <i>t</i> test.</p

The proportion of patients with a detectable viral load (≥400 copies/ml) at study visits using three viral load assays (Cavidi reverse transcriptase (RT) assay, Roche RNA PCR, and branched DNA assay [bDNA]).

<p>The proportion of patients with a detectable viral load (≥400 copies/ml) at study visits using three viral load assays (Cavidi reverse transcriptase (RT) assay, Roche RNA PCR, and branched DNA assay [bDNA]).</p

Characteristics of the Cavidi^® reverse transcriptase assay for detecting HIV viral loads ≥400 copies/mL using RNA PCR or branched DNA assay (bDNA) assays in patients receiving antiretroviral therapy.

a<p>95% CI, 95% Confidence Interval.</p>b<p>Sensitivity of the RT assay was the proportion of patients at baseline with RT assays ≥400 eq copies/ml among those with viral loads ≥400 copies/ml using RNA PCR or bDNA assays. Specificity of the RT assay was the proportion of patients at week 36 or 48 of treatment (which ever was the last value) with undetectable RT activity among those with viral loads <400 copies/ml using RNA PCR or bDNA assays. bDNA data from nine patients were excluded due to technical errors in one run.</p>c<p>Positive and negative predictive values were calculated using a 22% prevalence (18 of 83 patients with RNA PCR available after week 24) of a detectable RNA PCR viral load at week 36 or 48 of therapy; a sensitivity of 100% and specificity of 95% for the RNA PCR assay and a sensitivity of 100% and a specificity of 90% for the bDNA assay.</p

Flow chart of subjects with HIV viral loads conducted at baseline and follow-up after 24 weeks of antiretroviral therapy.

<p>(RT = Cavidi reverse transcriptase (RT) assay, Roche RNA PCR, and bDNA = branched DNA assay).</p

The distribution of CD4 cell count and HIV viral loads since initiation of antiretroviral therapy (study week 0).

<p>A. Distribution of CD4 cell count; B. HIV viral load by RNA PCR; C. HIV viral load by branched DNA (bDNA) assay; D. HIV viral load by Cavidi reverse transcriptase (RT) assay. Top and bottom of the boxes are 25th and 75th percentiles, respectively. Horizontal lines within the boxes indicate median values. Central vertical lines <i>(whiskers)</i> that extend from the boxes to the highest and lowest rates indicate the 95% and 5%, respectively. Dots indicate the individual values outside whiskers.</p