Effects of Formalin Fixation and Prolonged Block Storage on Detection of Hepatitis C Virus RNA in Liver Tissue

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Abstract
It has been suggested that prolonged formalin fixation and block storage adversely affect hepatitis C virus (HCV) ribonucleic acid (RNA) detection in tissue by reverse transcriptasepolymerase chain reaction (RT-PCR). We attempted to determine whether short-term perfusion fixation (3–5 days) or prolonged formalin storage adversely affects the detection of HCV RNA in paraffin-embedded tissue in comparison with 24-h fixation. Also, we examined the effects of prolonged storage of paraffin blocks on the sensitivity for HCV detection. We performed RT-PCR in formalin-fixed explanted livers from 20 liver allograft recipients known to be HCV positive (10 with specimens stored for 2–4 years and 10 with specimens stored for >4 years). We compared the results of perioperative needle liver biopsy specimens fixed overnight with liver sections fixed by perfusion for 3–5 days and bulk liver tissue stored in formalin for years (mean, 6.25 years; range, 2–11 years). HCV RNA was detected in 100%, 85%, and 0% of specimens fixed for 24 h, 3–4 days, and years, respectively. We conclude that HCV can be readily detected in tissue fixed by formalin overnight, sensitivity decreases slightly with intermediate-length fixation, and HCV is rendered undetectable by prolonged fixation. In addition, retention of formalin-fixed tissue in paraffin blocks does not affect the sensitivity of HCV detection.