Field study to determine the reliability of HIV viral load results shows minimal impact of delayed testing

Understanding factors that impact on the accuracy of HIV viral load (VL) results is key to quality improvements of VL programmes, particularly in resource limited settings. In this study we evaluated whether testing delay and room temperature storage (between 25-30°C) prior to testing affected results. 249 individuals who were on antiretroviral therapy, or with newly diagnosed HIV, were recruited and three PPT samples were collected from each patient. One sample was tested within 24 hours, while the others were stored un-centrifuged at ambient temperature prior to testing. Centrifugation and testing of matched samples were performed on days 4 and 7 after collection. In samples with initial VL >2 log copies/mL, time delay and ambient temperature storage had minimal impact. When grouped according to day 1 VL range, 96-100% of samples at day 4 and 93-100% at day 7 had a VL within 0.5 log copies/mL of the first result. Greatest variability was observed at day 4 and 7 when the day 1 VL was <2 log copies/mL, however, there was no trend of increasing difference with time. Of day 1 samples with undetectable VL or VL <50copies/mL, 80% and 78% had concordant results at days 4 and 7, respectively. Detection in later samples appeared to be stochastic, rather than showing a worsening trend. These results provide further evidence that VL is stable in PPT tubes for up to 7 days when stored at room temperature. It shows that there is significant variability in samples with VL close to the limit of detection, not affected by testing delay. Stochastic variation or technical factors that may increase the chance of false positive results could possibly account for this.