Quantification of hepatitis C virus RNA in serum by branched DNA-based signal amplification assays

The objective of the study was to compare the clinical sensitivity and spec ificity of versions 1.0 and 2.0 of the branched DNA (bDNA)-based hepatitis C virus (HCV) RNA quantification assay, and also to compare the values yiel ded by the two versions according to the HCV genotype. Serum samples from 2 68 patients tested routinely by a non-quantitative HCV RNA PCR assay (group A) were tested with version 2.0 of the bDNA assay. Samples from 342 HCV PC R-positive patients with chronic hepatitis C eligible for interferon treatm ent (group B) were tested with both version 1.0 and version 2.0 of the bDNA assay. Version 2.0 had a clinical sensitivity of 92% (95% confidence inter val (CI): 87-97%) in group A and 89% (86-92%) in group B. In group B, the g ain in sensitivity with bDNA 2.0 was 16% relative to bDNA 1.0 (P < 0.001). The log values of the two assays correlated with samples positive by both a ssays (P = 0.83, P < 0.0001), but the distribution of values was larger in samples containing HCV genotypes 2 and 3. The mean ratio of assay 2.0/assay 1.0 values was 1.69 +/- 1.44 (range: 0.33-13.43). The mean ratio was close to 1 with samples containing genotype 1 or 4, but ranged from 0.33 to more than 5. The mean ratio was dose to 3 with samples containing genotype 2 or 3, and ranged from 0.5 to more than 13. HCV RNA levels were significantly lower in samples containing genotype 4 than in those containing other genot ypes. Sera from 200 anti-HCV-negative, HCV RNA PCR-negative blood donors (g roup C), and from 164 anti-HCV-negative patients with symptoms of chronic l iver disease (group D) were used to assess the clinical specificity of bDNA 2.0. In addition, samples with an HCV RNA titer between 0.2 (assay cutoff) and 0.5 MEq/ml from a group of 546 patients tested routinely for HCV RNA l oad by bDNA 2.0 (group E) were retested by bDNA 2.0 and by qualitative PCR. The specificity of bDNA 2.0 was 100% (98-100%) in group C and 99% (97-100% ) in group D. Among the 41 samples from group E, 38 were positive by bDNA2. 0 retesting (36 were PCR-positive) and three were negative by bDNA2.0 retes ting (all were PCR-positive). It is concluded that version 2.0 of the bDNA assay is markedly more sensitive than version 1.0 and has a good specificit y. In contrast with version 1.0, version 2.0 is not influenced by the HCV g enotype. The relationship between values obtained with assays 1.0 and 2.0 o n clinical specimens is not linear, indicating that HCV RNA titers cannot r eliably be calculated from the results of version 1.0. (C) 1999 Elsevier Sc ience B.V. All rights reserved.