ASSESSMENT OF HEPATITIS-C VIREMIA USING MOLECULAR AMPLIFICATION TECHNOLOGIES - CORRELATIONS AND CLINICAL IMPLICATIONS

Objective: To compare two recently developed molecular techniques for quantitating the levels of hepatitis C virus (HCV) RNA in the serum of patients with a wide spectrum of chronic hepatitis C. Design: Serum s amples from 299 patients with HCV viremia, 101 control patients withou t HCV infection, and 19 consecutive patients receiving systemic interf eron therapy were evaluated by a commercially available branched-chain DNA (bDNA) assay and a quantitative competitive polymerase chain reac tion (PCR). Setting: University-based hepatology clinics and reference virology laboratory. Patients: Patients with HCV viremia as defined b y results of qualitative RNA PCR, including 53 HCV-infected blood dono rs, 34 patients receiving renal dialysis, and 212 patients attending a hepatology clinic. Results: Results of in vitro and in vivo experimen ts indicated that the sensitivity and dynamic range of the PCR assays were greater than those of the bDNA assay. Detection of HCV viremia by the bDNA assay was highly dependent on viral RNA titers, with a sensi tivity of 5% at HCV RNA titers of 5.0 logs per mL or less and 94% at t iters of 5.5 logs per mt or greater. The best correlation between assa ys was observed in specimens with HCV RNA titers between 6.0 and 7.5 l ogs per mL (r = 0.73). In patients with high-titer HCV viremia, includ ing liver transplant recipients and patients with cirrhosis, quantitat ive PCR results were an average of 12-fold higher than bDNA assay resu lts. Results of repetitive testing of discordant specimens showed that these discrepancies were caused by a high kit-to-kit coefficient of v ariation (112%) in the bDNA assay. Of 19 patients receiving interferon therapy, 9 (47%) became bDNA negative, but only 5 became quantitative PCR negative. The bDNA-negative, quantitative PCR-positive patients a ll had relapse when therapy was discontinued. Conclusions: The bDNA as say has a narrower linear range for quantitation of HCV viremia than q uantitative PCR. Because persons with low HCV titers may respond well to therapy, seropositive persons with negative bDNA results should be retested with PCR-based assays. Similarly, the bDNA assay may underest imate the true degree of HCV viremia in persons with endstage infectio n (>10(7) RNA equivalents/mL of sera). Despite these limitations, the combination of bDNA- and PCR-based assays appears to be optimal for se lecting and following patients during interferon therapy.