13th Annual Conference of the British HIV Association 29 March–1 April 2007, Brighton, UK

DRIED BLOOD SPOT (DBS) TESTING FOR VIROLOGICAL MONITORING IN HIV-INFECTED INDIVIDUALS RECEIVING FIRST LINE HAART IN UGANDA

HIV Med 2007 Mar 29-Apr 1 (Suppl 1);13:6 (abstract no. O23)

L Waters¹, A Kambugu², H Tibenderana², S Mandalia¹, D Meya², L John¹, M Nabankema², TC Quinn³, B Gazzard¹, SJ Reynolds³ and M Nelson^1
1St Stephen’s AIDS Trust, Chelsea and Westminster Hospital, London, UK, ²Infectious Disease Institute, Makerere University, Kampala, Uganda, ³National Institute of Allergy and Infectious Diseases, National Institutes of Health and Johns Hopkins University School of Medicine, Baltimore, USA

OBJECTIVES: Viral load (VL) monitoring is largely unavailable in Africa due to the cost and logistics. DBS samples have been used for VL quantification but have not been assessed in high volume clinic settings. We compare standard and DBS VL assays.

METHODS: Cross-sectional study of 402 patients established on first-line HAART. At 6 months, as well as local plasma VL (Roche Amplicor), whole blood (WB) was spotted on filter paper and dried. Samples were sent for RNA extraction (Primagen, Holland) and real-time PCR VL (Roche Taqman). DBS was compared with local plasma VL. After interim analysis cross-reactivity between cell-associated DNA in WB and HIV RNA was postulated as an explanation for the false positive rate; subsequently WB and plasma (PL) DBS were collected and, in the final phase, plasma alone.

RESULTS: A total of 402 subjects underwent standard and DBS VL yielding 306 WB and 218 PL samples (122 paired). By standard VL virological failure (>500 c/ mL) occurred in 39/402 (9.70%). WB DBS testing (n=306) yielded four false negative VLs (all <2000 c/mL by standard) and 64 false positives (50% <1000 c/mL; median 1002 c/mL). WB DBS VL>500 had a sensitivity/specificity/ positive and negative predictive values (95% CI) of 0.86 (0.67–0.96), 0.77 (0.71–0.81), 0.27 (0.18–0.46) and 0.98 (0.95–1.00) respectively. PL DBS (n=218) yielded one false positive result (593 c/mL). The sensitivity/specificity/PPV/NPV of PL DBS >500 were 1.00 (0.84–1.00), 0.99 (0.97–1.00), 0.95 (0.77–1.00) and 1.00 (0.77–1.00) respectively. Bland and Altman plots revealed observed agreement of 0.73 (0.64–0.81) between the paired WB and PL DBS results.

CONCLUSION: DBS testing may provide a practical method of VL monitoring in Africa. WB is associated with false positive results; using PL appears to negate this.

2007-03-29
O23

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