Potential Applications of Serum HBsAg Level Measurement in Patients with Hepatitis B and D Co- Infection

Pathogenesis of HDV infection is still insufficiently studied. Such marker of a HBV mono-infection disease activity as HBeAg rarely occurs in HDV co-infected patients. It is known that HDV infection is generally associated with a suppression of HBV replication [2]. In most cases the severity of CHD depends on the level of HDV RNA. A quantification of HDV RNA is done in specialized laboratories and this method is very expensive. Therefore, in clinical practice it is desirable to have some other markers which make it possible to estimate the HDV RNA level without measuring it directly. Recent data show that the HBsAg level in patients with a HBV mono-infection correlates with the covalently closed circular DNA (cccDNA) level in the liver [3]. Furthermore, it correlates with the transcriptional activity of cccDNA and is considered as a surrogate marker for the amount of infected cells [4,5]. Several studies show that HBsAg and HBV DNA levels vary strongly between the phases of CHB [3,6,7]. Without treatment, the serum HBsAg level changes slower than the HBV DNA level [4,6]. Today HBsAg level is used to distinguish between inactive carriers and patients with an active disease. However, the relationship between the HBsAg level and other markers of HDV activity in co-infected patients is still insufficiently studied. The importance of the HBsAg level monitoring during the interferon treatment was demonstrated in several studies [8,9]. Long-term interferon therapy can be envisaged in patients who exhibit a significant decline of HBsAg levels during initial therapy [10].