We quantitatively measured serum HBV load in 90 HBV infected patients with HCC and in 90 age- and gender-matched patients with HBV infection alone and found that HCC patients had higher serum HBV DNA level than patients without HCC, especially in the age range of 50-59 years or below 40 years. The data in the present study indicate that the patients with higher HBV level have more risk to develop HCC.
There were a few retrospective studies in which the authors compared HCC and non-HCC patients' HBV DNA level to clarify the role of HBV load in HCC development. Some authors stated the level in HCC patients was higher than that in non-HCC patients [14, 15] and > 104  or > 105  copies/ml HBV DNA level was supposed to be an independent risk factor of HCC development. As an indicator of active replication of HBV, the higher HBeAg positive rate is usually associated with an increased risk of HCC . Our findings were similar to these previously reported results. However, in Tsai et al's paper, there existed no significant difference in HCC and non-HCC patients' HBV DNA level . Another study performed in India showed that the HBV DNA load in HCC patients was lower than that of HBV-related chronic liver disease patients . However, in these two studies, the HCC group patients were both obviously older than the non-HCC group patients (53.7 ± 12.7 vs. 32.1 ± 10.0 years , 53.6 ± 13.2 vs. 44.2 ± 14.7 years ). The evolution and the viral load of HBV infection may be influenced by age at acquisition. In the present study, although it is difficult to determine duration of the infection for each patient, we considered that most patients in our study had been infected with HBV in their infantile or childhood periods as the majority of chronic HBV infection in China is due to the perinatal infections . Thus, the comparable patients' ages in the HCC and non-HCC groups may represent the similar infection durations in the two groups. Since HCC is a long-term outcome of chronic HBV infection and HBV DNA level is usually higher in younger CHB patients than in older ones , the matching of the patients' age is essential in the comparison of HBV DNA level in patients with or without HCC.
Large number chronic HBsAg carriers in Taiwan were followed up for a long period and the prospective data showed an increased risk for cirrhosis and for HCC with increasing level of HBV DNA [24, 25]. Several studies have suggested an increased risk of HCC with high HBV DNA level (> 106 copies/ml , 104-107 copies/ml  or > 105 copies/ml ). In our study, the data demonstrated that the patients with higher than 104 IU/ml HBV DNA level had more risk to be diagnosed as HCC, which was similar to the previous prospective reports [25–29]. The commonly used quantitative units of HBV DNA level in papers are IU/ml and copies/ml. In the current WHO HBV standard and consensus, one IU is approximately equivalent to five genome equivalents (copies) . The viral load of 104 IU/ml identified in this study is approximately equal to 5 × 104 copies/ml.