Background:  Viral load quantification is used for monitoring HIV infection in clinical routine and is usually carried out in plasma specimens. However, it can be made in other body fluids or in dried blood spots (DBS). The latter sample format may be especially useful for monitoring patients living in resource-poor settings.

Methods:  Pairwise plasma and DBS samples belonging to HIV-1-infected patients were quantified using 2 different commercial assays: Nuclisens EasyQ^®HIV-1 v1.1 (Biomerieux) and the m2000rt Real Time™HIV (Abbott). Nucleic acid extraction was performed manually using the Nuclisens Isolation kit (Boom methodology) and using the mSample Preparation kit (an iron particle based method). Statistical correlations were performed using SPSS v13.0.

Results:  A total of 103 paired plasma and DBS samples were collected. Viral load determinations could be made in 97 (94.2%) using Nuclisens and 81 (78.6%) using m2000rt. The correlation between measures in plasma and DBS was good, although better results were obtained using Nuclisens (R² = 0.87, p <0.001) than m2000rt (R² = 0.70, p <0.001). While the specificity was excellent and similar using both Nuclisens and m2000rt (97.1% vs 100%), the sensitivity was better using Nuclisens than m2000rt (75.8% vs 56.5%). Overall, viral load values in DBS tended to be lower than in plasma with mean (SD) differences of 0.3 (0.5) logs and 0.76 (0.8) logs using Nuclisens and m2000rt, respectively. The agreement between measurements in plasma and DBS was also assessed using a Bland-Altman plot for each assay. Nuclisens provided 95.9% of samples within its defined limits (–0.65 to 1.26), while m2000rt provided 100% within its limits (–0.8 to 2.33). However, the limit range for the latter is significantly wider. When comparing viral load determinations with Nuclisens and m2000rt, the correlation was good too, reaching R² = 0.921 (p <0.001) for plasma samples and R² = 0.714 (p <0.001) for DBS.

Conclusions:  HIV-1 viral load can be quantified accurately using DBS with either Nuclisens EasyQ HIV-1 or m2000rt Abbott RealTime HIV, although Nuclisens may outperform m2000rt at least when nucleic acids are extracted manually.