Hepatitis C virus: quantitation and distribution in liver.

The optimal method for viral quantitation and the most appropriate site for determining viral load in patients with chronic hepatitis C virus (HCV) infection are unknown. We developed a method for measuring HCV RNA in the liver with the following features: 1) efficient extraction of RNA from tissue (89% of RNA recovered); 2) accurate amplification using branched DNA with strong concordance between a single sample tested on multiple occasions either in the same or in different runs; 3) good sensitivity (95%) and specificity (100%). HCV RNA was detected in as little as 2 mg of tissue, and viral load determined in a needle biopsy was representative of viral load in other parts of the liver. Within individual livers, 68% of the samples quantitated were within 1.5-fold of the geometric mean, and 95% were within 2.2-fold of the geometric mean. The mean ratio of virus in the liver and serum was 103, range 17.4-286. A delay of 30 minutes before freezing the liver tissue resulted in a reduction in the measured viral load in some, but not all instances. A sensitive, specific and reproducible method for quantitating HCV RNA in the liver has been developed. Measurement of viral load at one site was representative of viral load at other sites. While hepatic HCV RNA levels are consistently greater than serum levels, the ratio of liver of serum viral load varies widely. The clinical use of measurement of viral load in the liver remains to be defined.