Hepatitis C virus RNA assays: a comparison of SuperQuant and Monitor

Hepatitis C RNA testing has been used extensively to assess the efficacy of antiviral therapy and has increasingly become an integral part of clinical management of patients with chronic hepatitis C. A variety of commercially available hepatitis C virus (HCV) RNA tests are used to detect HCV RNA qualitatively or quantitatively. These commercial tests have fundamental differences that are reflected on the values they generate. We compared two widely used assays, HCV SuperQuant (SQ) and Amplicor HCV Monitor (M1 and M2), in sera of patients with chronic hepatitis C. A total of 506 sera from 79 patients were tested with both assays. The data were logarithmically transformed and analyzed by linear regression and measurement of agreement. Two hundred thirty-eight sera had HCV RNA values within the dynamic range of both assays. The correlation between the assays was fair, with a correlation coefficient (r) of 0.699. Overall, SQ generated higher values than M1 with a mean difference of 0.558 log (SD = 0.624). One hundred ninety-four (38%) and 121 (24%) of the sera were below the dynamic range of M1 and SQ, respectively. Seventy-three sera, undetectable by M1, were positive by SQ. The Amplicor HCV Monitor 2.0 (M2) was performed in 66 sera. All were positive by SQ and M2, but only 38 were within the dynamic range of M1. The correlations between these tests were good (r = 0.68-0.78), but the agreement was rather poor. In conclusion, this study confirms that both SQ and M2 are more sensitive than M1. Additionally, our results show rather poor agreements between these assays. The recent attempts in standardizing the reporting of these assays should make their results more easily interchangeable.