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Editor,—Haydon et al (Gut1998;42:570–5) have found that hepatitis C virus (HCV) RNA is present in the liver of 87% of unselected patients with circulating anti-HCV antibody (confirmed by recombinant immunoblot assay) and negative serum HCV RNA by polymerase chain reaction (PCR). Furthermore, 70% of these patients had normal serum alanine aminotransferase (ALT) concentrations. Previous experience from both our group and others would suggest that most of these patients would be HCV RNA negative in liver tissue, whether treated or untreated.1-3 In fact, Fong and colleagues have shown that eight patients with anti-HCV antibody, persistently normal ALT concentrations (mean 14.5 months), and negative serum HCV RNA, had no HCV RNA detectable in liver or peripheral lymphocytes using qualitative reverse transcriptase (RT) PCR.2 Recently, we used a multi-cycle RT PCR (SuperQuant, National Genetics Institute, Culver City, CA, USA) to quantify HCV RNA in both liver and serum. Ten untreated patients with detectable anti-HCV antibody (including one patient who was coinfected with HIV) were negative in serum using the SuperQuant assay: eight of these patients had raised ALT concentrations, and all had a liver biopsy sample taken. Liver tissue samples were assayed for HCV RNA and nine patients were negative in liver tissue. Three additional patients had negative serum for HCV RNA (Roche Amplicor, Roche Molecular Systems) and had no detectable liver HCV RNA (SuperQuant). However, using the SuperQuant assay, small amounts of HCV RNA (all less than three logs) were found in their serum. We speculate that this more sensitive assay might have amplified extrahepatic viral sequences.4
Based on our data, we believe that most patients with negative HCV RNA in serum will be found to be HCV RNA negative in liver, particularly when ALT concentrations are normal. Furthermore, very sensitive assays may detect small quantities of HCV RNA (which may be extrahepatic in origin) in serum but not in liver.4
Editor,—We thank Drs Bonacini and Redeker for their interesting comments and data. Their study, which used a multi-cycle RT PCR assay with a detection sensitivity of 100 copies HCV RNA/ml serum, showed that only one patient out of 10 with detectable anti-HCV antibody was positive in liver tissue, when concurrently negative in serum.
Using a limiting dilution assay (which has already been proved to have significant reproducibility when multiple samples are tested in duplicate, and a significant correlation with three commercial assays1-1) with a detection sensitivity of 80 HCV copies/ml of serum (in a 5 ml sample of serum), we showed that 10 out of 12 patients who were RT PCR negative in serum, were RT PCR positive in liver. Significantly, all 12 patients had ongoing inflammation, diagnosed by diagnostic laparoscopy and from liver biopsy samples.
We would be interested to know the histological findings taken from the liver biopsy samples in Dr Bonacini’s study; ongoing hepatic inflammation indicates the continued presence of the virus in very small quantities. We maintain our hypothesis that such patients are viraemic below the detection sensitivity level of the above assays (which is similar, although the assays have not been compared), and that it is impossible to be certain that the infection has been cleared completely even at a detection sensitivity of 100 copies HCV/ml.
However, the prognostic importance of these data is that serum RT PCR negative patients, with chronic HCV infection, need to be followed up for an indefinite period because there is no indication that they are immune from progressive liver disease in the future.
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