This prospective study was conducted over a period of one year from 2008 to 2009 in the Department of Transfusion Medicine, The Tamilnadu Dr. MGR Medical University, Guindy, Chennai, India. A total of 9100 voluntary blood donors were selected. This study was approved by the ethical committee of the institution and a written informed consent was obtained from the donors. 5ml of blood from each donor was collected from the collection bag into a sterile capped tube. It was then centrifuged and the plasma was separated and stored as two aliquots at -70°C till further use.

The samples that were frozen earlier were thawed and used. The screening for the Hepatitis B core antibody (anti-HBc IgM and IgG) was done by a 3rd generation ELISA by using Biorad’s Monolisa Anti-HBc Plus kit. It is an indirect type of ELISA which is based on the use of a solid phase which is prepared with the recombinant HBc antigen. All the steps were followed as per the manufacturer’s instructions.

The screening for the Hepatitis B surface Antigen (HBsAg) was done by a 3rd generation ELISA by using J.Mitra’s Hepelisa kit.

The detection of the HBV DNA in the Hepatitis B core antibody positive samples was done by real time PCR by using a Roche light cycler. The DNA was extracted from the plasma by using a QIAamp DNA kit from Qiagen (Germany). All the steps were followed according to the manufacturer’s instructions.

The statistical analysis was done by using the SPSS software. For relating the variables with each other, a multivariate analysis was done. The Chi square test was employed to detect any significant correlation between the different variables.

Among the total 9100 donors in the study, 8399 (92.29%) were males and 701(7.7%) were females. Of the total 9100 donor blood samples which were tested for anti-HBc (IgM and IgG), 911 samples (10.01%) were found to be positive and 199 samples (2.18%) were found to be positive for HBsAg. Out of 199 HBsAg positive samples, 91 were positive for the core antibody [Table/Fig-1]. So, 820 samples were positive for the core antibody alone and they were negative for HBsAg. The gender distribution and the age group distribution of the anti-HBc antibody has been shown in the [Table/Fig-2 & 3] respectively.

The 820 samples which were positive for the core antibody and negative for HBsAg were subjected to Real time PCR (RT-PCR) for the HBV-DNA detection. Of the 820 samples, 2 samples (0.24%) were found to be positive for the HBV-DNA.

The blood donors who are chronically infected with HBV but without detectable levels of the Hepatitis B surface Antigen (HBsAg) and with or without antibodies to the Hepatitis B core Antigen (Anti-HBc) contribute to the residual risk of the transfusion transmitted HBV infection.

In our study, of the 9100 blood donors who were tested for the Hepatitis B core antibody, 911 (10.01%) were positive. Of the 911 core antibody positive donors, 820 donors were HBsAg negative, whereas the remaining 91 were HBsAg positive. The varied prevalence of the core positivity has been reported in Indian studies. Dhawan et al., [5] from Chandigarh reported a core positive rate of 8.4% which was comparable to our data, whereas a high positivity rate of 18.3% was observed by Bhattacharya et al., [6] in West Bengal [Table/Fig-4].

The demographic analysis of the 911 donors who were positive for the anti-HBc antibody showed that it had a higher preponderance in males (10.07% in males vs 9.27% in females; p=0.32; [Table/Fig-2]. A study which was done by Asim et al showed a difference in the seroprevalence of the core antibody between the male and the female donors (19.3% vs 18%), but as in our study, the difference was statistically not significant [7]. We observed a significantly increasing prevalence of the core antibody with the increasing age of the donor population [Table/Fig-3], which was similar to the findings of the study which was done by Seo et al., [8]. In our study, 2.18% of the donors were positive for HBsAg. This was in concordance with the study which was done by Bharat et al., in New Delhi, who had reported a 2.2% seropositivity for HBsAg in the blood donors [2].

In our study, of the 820 samples that were positive for the anti-HBc antibody and negative for HBsAg, 2 (0.24%) samples were found to have HBV-DNA positivity by the RT-PCR method. Makroo et al reported 0.15% of the core antibody positive samples to have the HBV DNA [9]. Gutierrez et al., from Venezulla reported a 6% prevalence of the HBV-DNA in samples which were positive for anti-HBc, only when the titres of the antibody was equal to or higher than 1/10 [10]. Kleinman et al reported a 0.24% detection rate of the HBV-DNA among the anti-HBc reactive donors [11]. Amini et al., in a study which was done on 4930 healthy blood donors, found that 5.1% were positive for anti-HBc without having any detectable HBsAg; however, they did not determine the presence of the HBV-DNA [12]. The reasons for the non detection of the HBV DNA in the samples may be that the donor may have been in the recovery phase of an acute infection or that the donor may have been immune due to an earlier infection and with undetectable levels of HBV-DNA now.

A donor with a positive anti HBc-IgG indicates either a past infection or a carrier state. The anti-HBc IgG may remain positive for life in an affected individual, although the individual has protective levels of anti-HBs and therefore, this does not necessarily mean that the blood of such a donor is infectious. However, unless we do a sensitive Nucleic Acid Amplification Test (NAT), we can’t confirm the presence or absence of the virus in such a donor. But in a majority of the blood banks in the developing countries like India, NAT may not be feasible. Unlike IgG anti-HBc, the IgM core antibody is a marker of a recent Hepatitis B infection. Sawke et al felt that the screening of the donor blood for the total anti-HBc was not practical, as it could result in the discarding of huge amounts of blood, whereas the screening for the IgM- anti- HBc of the blood units which were negative for HBsAg could identify the potentially infectious units [13].

These observations suggested that the HBV DNA screening would be more effective in preventing the transfusion transmitted Hepatitis B infections. But the anti-HBc screening would be a good screening marker where the NAT screening is not feasible. But due to the varying specificities of the current antibody screening assays, the absence of an acceptable confirmatory test strategy and the high anti-HBc seroprevalence rates in the HBV endemic regions make the screening problematic due to the high donor loss rates.

This study helps in determining the current status of the Hepatitis B infection and the prevalence of the occult HBV infection in our blood donor population. The screening of the blood units for the core antibody adds to the cost, but it is definitely useful in reducing the residual risk of post transfusion hepatitis. Though the HBV DNA was detected only in 0.24% of the core antibody positive donors, they were still considered as infectious unless they were proved as negative by PCR for the HBV DNA. Considering the loss of the donor pool due to the high prevalence rate of anti-HBc among the voluntary blood donors in our study, the subject of including the anti-HBc testing as a routine screening test is debatable.