Determination of HIV-1 viral load on dried blood spot specimens

Dried blood spot specimens on filter paper were evaluated to determine the viral load of the human immunodeficiency virus type 1 (HIV-1), through the Cobas®Ampliprep/Cobas®Taqman® HIV-1 test. RNA levels were quantified in pairs of plasma and dry blood spot specimens on filter paper from persons infected with HIV-1. The Pearson linear correlation coefficient was calculated as well as the agreement by the Bland-Altman method. Studies on precision, linearity and analytical sensitivity of the assay were also carried out. The linear regression model was used to predict the value of the viral load in the plasma. There was a high correlation in viral load measurements in the plasma and dried blood spot specimens, in 39 out of the 43 sample pairs studied (r = 0.964, p < 0.0001). Detection rate was 90.7 % and the test behaved linearly between 134 and 420 000 copies/mL of viral RNA, showing good precision. No statistically significant differences were observed between the means of the true and predicted values of viral load in the plasma, with a 95 % confidence level. These results support the use of dried blood spots on filter paper for viral load determination with the Cobas®Ampliprep/Cobas®Taqman® HIV-1 Test. Authors recommend the validation of the model proposed with a larger number of samples.