HIV This Week

Evaluation of a dried blood spot HIV-1 RNA program for early infant diagnosis and viral load monitoring at rural and remote healthcare facilities

Lofgren SM, Morrissey AB, Chevallier CC, Malabeja AI, Edmonds S, Amos B, Sifuna DJ, von Seidlein L, Schimana W, Stevens WS, Bartlett JA, Crump JA. AIDS. 2009 23(18):2459-66.

Lofgren and colleagues set out to assess technical and operational performance of a dried blood spot-based HIV-1 RNA service for remote healthcare facilities in a low-income country. A method comparison and operational evaluation of dried blood spot RNA against conventional tests for early infant diagnosis of HIV and HIV RNA quantitation under field conditions in Tanzania was conducted. Dried blood spots were prepared and plasma was frozen at -80 degrees C. Dried blood spots were mailed and plasma couriered to a central laboratory for testing using the Abbott m2000 system. Infant diagnosis dried blood spots were also tested for HIV-1 DNA by ROCHE COBAS AmpliPrep/COBAS TaqMan System. Results of dried blood spot RNA were compared with conventional tests; program performance was described. Among 176 infant diagnosis participants, using a threshold of at least 1000 copies/ml, sensitivity and specificity of dried blood spot versus plasma RNA were 1.00 and 0.99, and of dried blood spot RNA versus dried blood spot DNA were 0.97 and 1.00. Among 137 viral load monitoring participants, when plasma and dried blood spot RNA were compared, r value was 0.9709; r value was 0.9675 for at least 5000 copies/ml but was 0.7301 for less than 5000 copies/ml. The highest plasma RNA value at which dried blood spot RNA was not detected was 2084 copies/ml. Median (range) turnaround time from sample collection to result receipt at sites was 23 (4-69) days. The Tanzania mail service successfully transmitted all dried blood spot and results between sites and the central laboratory. Under program conditions in Tanzania, dried blood spot provided HIV-1 RNA results comparable to conventional methods to remote healthcare facilities. The authors propose dried blood spot RNA testing as an alternative to liquid plasma for HIV-1 RNA services in remote areas

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Editors’ note: In this study, the weekly cost of mailing dried blood spot specimens from healthcare facilities to the central laboratory was 6$ compared to a weekly ground transport of frozen plasma samples on dry ice of 515$. The excellent sensitivity and specificity results for paediatric HIV diagnosis reported for dried blood spot specimens here, combined with a reasonable turnaround time for results in the absence of electronic or fax communications, suggests that cost-effectiveness analyses should be quickly undertaken. The earlier that infants with HIV infection are diagnosed, the sooner they can be placed on treatment .

Smith DM, May SJ, Pérez-Santiago J, Strain MC, Ignacio CC, Haubrich RH, Richman DD, Benson CA, Little SJ. AIDS. 2009; 23:2151-8.

To develop less costly methods to virologically monitor patients receiving antiretroviral therapy, the authors evaluated methods that use pooled blood samples and quantitative information available from viral load assays to monitor a cohort of patients on first-line antiretroviral therapy for virologic failure. They evaluated 150 blood samples collected after 6 months of therapy from participants enrolled in a San Diego primary infection program between January 1998 and January 2007. Samples were screened for virologic failure with individual viral load testing, 10 x 10 matrix pools and minipools of five samples. For the pooled platforms (matrix and minipools), the authors used a search and retest algorithm based on the quantitative viral load data to resolve samples that remained ambiguous for virologic failure. Viral load thresholds were more than 500 and more than 1500 copies/ml for the matrix and more than 250 and more than 500 copies/ml for the minipool. Efficiency, accuracy and result turnaround times were evaluated. Twenty-three percent of cohort samples were detectable at more than 50 HIV RNA copies/ml. At an algorithm threshold of more than 500 HIV RNA copies/ml, both minipool and matrix methods used less than half the number of viral load assays to screen the cohort, compared with testing samples individually. Both pooling platforms had negative predictive values of 100% for viral loads of more than 500 HIV RNA copies/ml and at least 94% for viral loads of more than 250 HIV RNA copies/ml. In this cohort, both pooling methods improved the efficiency of virologic monitoring over individual testing with a minimal decrease in accuracy. These methods may allow for the induction and sustainability of the virologic monitoring of patients receiving antiretroviral therapy in resource-limited settings.

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Editors’ note: Pooling strategies mix 5, 10, or more samples together for testing. If the pool is positive then each sample in the pool is tested to see which one(s) is (are) responsible. Viral load monitoring for patients on antiretroviral treatment is not recommended or performed in most resource-limited settings where the focus has been on getting more people in need on treatment. Adaptation of assays in current clinical use for settings with diverse HIV subtypes would allow the kinds of efficiency gains described here. The objective would be improved clinical outcomes and limits on the development of drug resistance.