Analytical and clinical sensitivity of the Procleix Ultrio HIV-1/HCV/HBV assay in samples with a low viral load

The Procleix Ultrio human immunodeficiency virus type 1 (HIV-1)/hepatitis C virus (HCV)/hepatitis B virus (HBV) (Ultrio) assay simultaneously detects HIV-1 RNA, HCV RNA and HBV DNA in individual blood donations. The main objective of the study was to assess the analytical and clinical sensitivity of the multiplex and discriminatory probe assays in samples with a low viral load.

The VQC HIV RNA genotype B, HCV RNA genotype 1 and HBV DNA genotype A standard dilutions were tested in 26 repeats. The probability of detection by Ultrio was compared with previously obtained data of the Procleix Duplex HIV-1/HCV assay on the same reference panels. A selection of 121 anti-HIV-1, 138 anti-HCV and 190 HBsAg positive samples from patients receiving antiviral therapy were tested. The majority of patient samples had a viral load below the detection limit of the diagnostic nucleic acid test assays, which made them suitable to evaluate the performance of the multiplex and discriminatory assays on yield cases with a similar low viral load.

The 95% and 50% detection end-points of the Ultrio assay along with the corresponding 95% confidence intervals are 53.7 (32.9-117.2) and 8.6 (6.2-12.1) geq/ml for HIV-1 RNA, 30.3 (19.0-62.4) and 5.2 (3.7-7.2) geq/ml for HCV RNA and 393.7 (147.9-6978) and 54.5 (22.4-143.8) geq/ml for HBV DNA. The analytical sensitivity of Ultrio expressed as a potency factor relative to previously obtained Duplex results on the same HIV-1 RNA and HCV-RNA standard dilutions was 1.09 (0.20-6.10) and 1.11 (0.21-5.89), respectively. The assay detected all 22 HIV-1 infected patients with viral load > 50 copies/ml, and 41 of 99 patients (41%) with viral load < 50 copies/ml, of which 23 (56%) were detected by the discriminatory assay. All 47 patients with HCV RNA load > 521 IU/ml and 10/91 polymerase chain reaction-negative patients with viral load < 50 IU/ml tested positive in Ultrio assay of which five were missed in the discriminatory test. The assay detected 53/55 HBV infected patients (96%) with viral load > 250 copies/ml and 108/135 patients (80%) with viral load < 250 copies/ml of which 17 (16%) were missed by the discriminatory test.

The new Procleix Ultrio assay is as sensitive as the Procleix Duplex assay for HIV-1 and HCV detection meeting the requirements of universal guidelines. The ability of the assay to detect HBV DNA in low viral load samples could be useful for screening blood. Inevitable negative results of discriminatory probe assays caused by stochastic sample variation will reduce the chance of recognizing low viraemic blood donors detected by individual donation nucleic acid test.