Improved detection of hepatitis B virus surface antigen by a new rapid automated assay

Laboratory Diagnosis and Monitoring of Viral Hepatitis

Many microbes, toxins, autoimmune diseases, and neoplastic diseases may cause liver inflammation; however, 5 viruses whose main pathogenesis is liver disease are referred to as hepatitis A, B, C, D, and E viruses. These viruses cause a significant burden of global illness. With the exception of hepatitis A virus, all may cause chronic infection potentially leading to cirrhosis and hepatocellular carcinoma. Excellent serologic and nucleic acid detection methods are available for determining the precise cause and, in some cases, the duration of infection. Diagnostics are critical for identifying individuals needing treatment and for monitoring the treatment success.

Introduction of an automated system for the diagnosis and quantification of hepatitis B and hepatitis C viruses

Hepatitis B virus (HBV) and Hepatitis C virus (HCV) infections pose major public health problems because of their prevalence worldwide. Consequently, screening for these infections is an important part of routine laboratory activity. Serological and molecular markers are key elements in diagnosis, prognosis and treatment monitoring for HBV and HCV infections. Today, automated chemiluminescence immunoassay (CLIA) analyzers are widely used for virological diagnosis, particularly in high-volume clinical laboratories. Molecular biology techniques are routinely used to detect and quantify viral genomes as well as to analyze their sequence; in order to determine their genotype and detect resistance to antiviral drugs. Real-time PCR, which provides high sensitivity and a broad dynamic range, has gradually replaced other signal and target amplification technologies for the quantification and detection of nucleic acid. The next-generation DNA sequencing techniques are still restricted to research laboratories.The serological and molecular marker methods available for HBV and HCV are discussed in this article, along with their utility and limitations for use in Chronic Hepatitis B (CHB) diagnosis and monitoring.

[Evaluation of HBs Ag, HCV and HIV Ag-Ab Assays using Bio-Rad Elite Microplate Analyzer.]

BACKGROUND

In this study, we evaluated the performance of Elite microplate analyzer (Bio-Rad Laboratories, France) and the related assays (ULTRA line) for the detection of hepatitis B virus (HBV), hepatitis C virus (HCV) and human immunodeficiency virus (HIV).

METHODS

Seroconversion panels, HBsAg positive/HBsAg negative (n=99/n=1,422), anti-HCV positive/negative (n=97/n=1,670), and anti-HIV positive/negative (n=112/n=1,704) samples were used to evaluate the performance of Monolisa HBsAg ULTRA, Monolisa HCV Ag-Ab ULTRA, and Genscreen ULTRA HIV Ag-Ab, respectively. The agreement of Elite microplate analyzer with CODA analyzer (Bio-Rad Laboratories, CA, USA) was also evaluated.

RESULTS

The detection limit of Monolisa HBsAg ULTRA was 0.034 IU/mL. For Monolisa HBsAg ULTRA, Monolisa HCV Ag-Ab ULTRA, and Genscreen ULTRA HIV Ag-Ab, diagnostic sensitivities were all 100%, diagnostic specificities were 100%, 99.8% and 99.9%, and total CVs (coefficients of variation) were 13.8-17.5%, 3.4-5.2%, and 7.5-9.5%, respectively. The agreement of Elite microplate analyzer with CODA analyzer was 99.5%.

CONCLUSIONS

The performance of Elite microplate analyzer and the related assays on analytical sensitivity, precision, early detection, diagnostic sensitivity and specificity was all adequate for a mass screening. However, further large multi-center studies should be performed to validate our results.

Comparison of the technical and clinical performance of the Elecsys HBsAg II assay with the Architect, AxSym, and Advia Centaur HBsAg screening assays

South East Asia has some of the highest prevalence rates of hepatitis B virus (HBV) infection (>or=8%) in the world, and the emergence of hepatitis B surface antigen (HBsAg) mutant strains is a growing problem. Assays with the highest levels of sensitivity, including mutant detection, should be used for routine HBsAg screening. In this large multicenter study, the clinical and technical performance of the fully automated Elecsys HBsAg II assay was compared with the Architect, AxSYM, and Advia Centaur HBsAg assays for HBsAg screening. Nine laboratories (three each from Thailand, Korea, and Singapore) compared the Elecsys HBsAg II assay with their routine HBsAg screening assay against a range of stored and routine clinical samples, including recombinant mutants. The Elecsys HBsAg II assay demonstrated equivalent sensitivity and specificity to the Architect HBsAg assay. However, the Elecsys HBsAg II assay recognized a native mutant sample (L94S, L97V, L98V, T123A) that the Architect HBsAg assay failed to detect. The AxSYM and Advia Centaur HBsAg assays appeared less sensitive for the detection of early HBV infection and also failed to detect some of the recombinant mutant strains. There was almost complete agreement between the Elecsys HBsAg II assay and comparator assays with respect to routine serum samples. The results of this study demonstrate that the Elecsys HBsAg II assay is a highly sensitive and specific screening assay for HBsAg and detects reliably the most important and clinically relevant HBV mutants and genotypes. It is suitable for routine HBsAg screening in Asia.

A novel nucleotide insertion in S gene of hepatitis B virus in a chronic carrier

Hepatitis B virus DNA was extracted from serum of a chronic carrier and polymerase chain reaction was performed on S gene. Direct sequencing showed a variant HBsAg with additional 4-amino acid insertion, and clone sequencing confirmed the mixture of variant HBsAg and wildtype HBsAg. Of 16 clones with 12-nucleotide insertion, 15 clones had identical AGAACAACACAA insertion between nucleotide 494 and nucleotide 495, and one clone had GGAACAACTCAA insertion in the same position plus 3-nucleotide deletion from nucleotide 491 to nucleotide 493. S114T, C121Y, T126S/A, Q129K, G130R, T131N, M133T, G145R, N146D substitution and premature stop codon were also found in those clones. However, the origin of HBV with 4-amino acid insertion in HBsAg was unclear.

The underlying mechanisms for the "isolated positivity for the hepatitis B surface antigen (HBsAg)" serological profile

During HBV infection, four structural antigen/antibody systems are observed: hepatitis B surface antigen (HBsAg) and its antibody (anti-HBs); the pre-S antigens associated with HBsAg particles and their antibodies; the particulate nucleocapsid antigen (HBcAg) and anti-HBc; and an antigen structurally related to HBcAg, namely HBeAg and its antibody (anti-HBe). Through the examination of this antigen-antibodies system, hepatitis B infection is diagnosed and the course of the disorder may be observed. Isolated HBsAg seropositivity is a peculiar serological pattern in HBV infection observed some times in routine laboratory. In most cases is not clear how this profile should be interpreted neither its significance. This pattern, however, may be associated with some clinical and laboratorial situations of great relevance, some of which will be addressed in this article.

Development of a sensitive enzyme-linked immunosorbent assay for detection of hepatitis B surface antigen using novel monoclonal antibodies

Hepatitis B virus (HBV) infection is the 10th leading cause of death worldwide. The most important diagnostic and screening marker for HBV infection is Hepatitis B surface antigen (HBsAg), and the most widely used HBsAg screening test is Enzyme-linked Immunosorbent Assay (ELISA). In this study, an ELISA assay has been developed for detection of HBsAg using two novel monoclonal antibodies (mAb) as capture layer and a polyclonal biotinylated Ab as detector phase. We evaluated the sensitivity, specificity, detection limit, seroconversion time, positive and negative predictive values and reproducibility of our assay with standard panels and different serum samples. The results were compared with a well established commercial kit. Both assays showed similar detection limit values of 0.5 to 0.7 ng/ml and the same seroconversion periods of 42 and 65 days for "ad" and "ay" serotypes of HBsAg, respectively. Sensitivity and specificity of the assay were 98.98% and 99.6%, respectively. The positive and negative predictive values of our assay were also calculated as 99.49% and 99.2%, respectively. Analysis of reproducibility of the present assay demonstrated 3.96% and 5.85% intra-and inter-assay coefficient of variations, respectively, which were less than those obtained by the commercial kit. There was a highly significant correlation between our designed assay and the commercial ELISA kit (p < 0.0001, r = 0.957). Altogether, our results indicate that the designed assay is comparable to the commercial kit in terms of sensitivity, specificity, positive and negative predictive values and reproducibility and could be employed for diagnosis of HBV infection in blood samples.

Hook's effect - a rare presentation in HBsAg screening

Detection of Hook's effect, the false negative results in HBs Ag immunoassay screening. Two drops of donor's serum was added to the sample well of hepacard device using a dropper and was allowed to react for 20 minutes and results read thereafter. The hepacard device when read after 20 minutes showed only one distinct pink test line and no control line. Serial dilutions (1:10, 1: 20) of the donors sample in normal saline was done and the test was re-run. Sample in 1: 10 dilution showed both control and faint pink test line, which intensified to pink band in 1: 20 diluted sample. The goal in the immunoassay detection of HBsAg should be to minimize erroneous results; so as not to endanger patient health and the blood supply.

Exceptional genetic variability of hepatitis B virus indicates that Rwanda is east of an emerging African genotype E/A1 divide

In Western Africa, hepatitis B virus (HBV) genotype E predominates throughout a vast crescent spanning from Senegal to Namibia and at least to the Central African Republic to the East. Although from most of the eastern parts of sub-Saharan Africa only limited sets of strains have been characterized, these belong predominantly to genotype A. To study how far the genotype E crescent extends to the East, a larger number of HBV strains from Rwanda were analyzed. Phylogenetic analysis of 45 S fragment sequences revealed strains of genotypes A (n = 30), D (n = 10), C (n = 4), and B (n = 1). Twelve genotype A sequences formed a new cluster clearly separated from the reference strains of the known sub-genotypes. Thus, with four genotypes and at least six sub-genotypes and a new cluster of genotype A strains, HBV shows an exceptional genetic variability in this small country, unprecedented in sub-Saharan Africa. Despite this exceptional genetic variability, not a single genotype E virus was found indicating that this country does not belong to the genotype E crescent, but is east of an emerging African genotype E/A1 divide.

A low steady HBsAg seroprevalence is associated with a low incidence of HBV-related liver cirrhosis and hepatocellular carcinoma in Mexico: a systematic review

To address the relationship between hepatitis B virus (HBV) endemicity and HBV-related liver diseases in Mexico. Research literature reporting on HBsAg and antibody to hepatitis B core antigen (anti-HBc) prevalence in Mexican study groups were searched in NLM Gateway, PubMed, IMBIOMED, and others. Weighted mean prevalence (WMP) was calculated from the results of each study group. A total of 50 studies were analyzed. Three nationwide surveys revealed an HBsAg seroprevalence of less than 0.3%. Horizontal transmission of HBV infection occurred mainly by sexual activity and exposure to both contaminated surgical equipment and body fluids. High-risk groups exposed to these factors included healthcare workers, pregnant women, female sex workers, hemodialysis patients, and emergency department attendees with an HBsAg WMP ranging from 1.05% (95% confidence interval [CI], 0.68-1.43) to 14.3% (95% CI, 9.5-19.1). A higher prevalence of anti-HBc in adults than those younger than 20 years was associated with the main risk factors. Anti-HBc WMP ranged from 3.13% (95% CI, 3.01-3.24) in blood donors to 27.7% (95% CI, 21.6-33.9) in hemodialysis patients. A heterogeneous distribution of HBV infection was detected, mainly in native Mexican groups with a high anti-HBc WMP of 42.0% (95% CI, 39.5-44.3) but with a low HBsAg WMP of 2.9% (95% CI 2.08-3.75). Estimations of the Mexican population growth rate and main risk factors suggest that HBsAg seroprevalence has remained steady since 1974. A low HBsAg prevalence is related to the low incidence of HBV-related liver cirrhosis and hepatocellular carcinoma (HCC) previously reported in Mexico.

A novel hepatitis B virus surface antigen immunoassay as sensitive as hepatitis B virus nucleic acid testing in detecting early infection

BACKGROUND

The aim was to considerably enhance the sensitivity of hepatitis B virus (HBV) surface antigen (HBsAg) detection and investigate whether the window period for HBV detection could be reduced.

STUDY DESIGN AND METHODS

A high-sensitivity chemiluminescent enzyme immunoassay (CLEIA) was developed for quantitative HBsAg detection by a combination of monoclonal antibodies, each one for a specific epitope of HBsAg, and by improving the conjugation technique. The sensitivity of the assay was compared with that of the existing chemiluminescent immunoassay (CLIA). Commercially available seroconversion panels and samples of HBV-infected chimpanzees were tested with the developed prototype to assess whether the window period for HBsAg detection could be reduced to that for DNA detection.

RESULTS

Compared to the existing CLIA, the CLEIA prototype detected HBsAg with approximately 230-fold higher sensitivity and showed a reduced window period. HBsAg detection by the CLEIA prototype and HBV DNA detection by polymerase chain reaction (PCR) occurred simultaneously. The mean time for the CLEIA prototype to first detect HBsAg was approximately 17.4 days less than that for the existing systems. Further, CLEIA prototype enabled HBsAg detection even in anti-HBs-positive seroconversion samples. In the inoculated chimpanzees the HBsAg and HBV DNA became detectable simultaneously and concentrations increased in parallel, whereas HBsAg remained detectable longer than HBV DNA in the declining phase of viremia.

CONCLUSION

The CLEIA prototype yielded results comparable with those of HBV DNA PCR. This novel high-sensitivity assay may be useful for early detection of HBV infection and monitoring patients with a history of infection.

Diagnosis and management of chronic viral hepatitis: antigens, antibodies and viral genomes

Virological tools, including serological and molecular tools, are needed to diagnose chronic hepatitis B and C infections. They may also be useful to establish their prognosis, but they have found their principal application in guiding treatment decisions and assessing the virological responses to therapy. The goal of chronic hepatitis B therapy is to prevent progression of liver disease. This is achieved if HBV replication is durably abolished or significantly reduced. In HBeAg-positive patients, HBeAg clearance followed by the HBe seroconversion phase can be achieved. In HBeAg-negative patients, long-term antiviral suppression of viral replication is needed. The loss of HBsAg, eventually associated with an HBs seroconversion, is the most desirable endpoint of therapy but is rarely achieved. The efficacy endpoint of chronic hepatitis C treatment is the sustained virological response, defined by an undetectable HCV RNA in serum with a sensitive assay 24 weeks after the end of treatment. The HCV genotype and on-treatment viral kinetics can be used to tailor treatment dosages and duration.

Genotyping and genomic sequencing in clinical practice

The global prevalence of chronic hepatitis B and its associated serious sequelae demand technologically advanced techniques of management. Nucleic acid testing (NAT) plays a key role in the diagnosis, surveillance, and treatment of chronic hepatitis B. NAT includes quantitative PCR-based HBV DNA assays, HBV genotyping, tests for mutations associated with resistance to antiviral medications, and assays to detect precore and core promoter mutations. This article reviews the uses of NAT in the diagnosis and management of chronic hepatitis B.

Multicenter study of a new fully automated HBsAg screening assay with enhanced sensitivity for the detection of HBV mutants

In a multicenter study a new, fully automated Roche Diagnostics Elecsys HBsAg II screening assay with improved sensitivity to HBsAg mutant detection was compared to well-established HBsAg tests: AxSYM HBsAg V2 (Abbott), Architect HBsAg (Abbott), Advia Centaur HBsAg (Bayer) Enzygnost HBsAg 5.0 (Dade-Behring), and Vitros Eci HBsAg (Ortho). A total of 16 seroconversion panels, samples of 60 HBsAg native mutants, and 31 HBsAg recombinant mutants, dilution series of NIBSC and PEI standards, 156 HBV positive samples comprising genotypes A to G, 686 preselected HBsAg positive samples from different stages of infection, 3,593 samples from daily routine, and 6,360 unselected blood donations were tested to evaluate the analytical and clinical sensitivity, the detection of mutants, and the specificity of the new assay. Elecsys HBsAg II showed a statistically significant better sensitivity in seroconversion panels to the compared tests. Fifty-seven out of 60 native mutants and all recombinant mutants were found positive. Among 156 HBV samples with different genotypes and 696 preselected HBsAg positive samples Elecsys HBsAg II achieved a sensitivity of 100%. The lower detection limit for NIBSC standard was calculated to be 0.025 IU/ml and for the PEI standards ad and ay it was <0.001 and <0.005 U/ml, respectively. Within 2,724 daily routine specimens and 6.360 unselected blood donations Elecsys HBsAg II showed a specificity of 99.97 and 99.88%, respectively. In conclusion the new Elecsys HBsAg II shows a high sensitivity for the detection of all stages of HBV infection and HBsAg mutants paired together with a high specificity in blood donors, daily routine samples, and potentially interfering sera.

Hepatitis B virus DNA in unusual serological profiles of hepatitis B surface antigen-positive sera

On the basis of a seroepidemiological survey of hepatitis B virus (HBV) infection conducted on 6208 random serum samples from four provinces of Thailand, we found 19 of 246 (7.7%) hepatitis B surface antigen (HBsAg)-positive samples with unusual serological constellations of HBV infection. Ten samples tested positive for HBsAg, anti-HBc (anti-hepatitis B core antibody), and anti-HBs (anti-hepatitis B surface antibody) markers (group I), 3 specimens were HBsAg and anti-HBs positive without detectable anti-HBc (group II), and the remaining 6 specimens showed only HBsAg (group III). In group I, 7 of 10 HBsAg-positive sera could be confirmed by HBsAg neutralization, yielding positive results for all samples. None of the group II sera were available in sufficient amounts for confirmation. In group III, five of six sera were confirmed by HBsAg neutralization, with four showing a positive reaction. HBV DNA was detected in 7 of 10 (70%) specimens in group I, in 1 of 3 (33.3%) specimens in group II, and in 3 of 6 (50%) specimens in group III. On the basis of HBsAg neutralization, HBV DNA was found in five of seven (71.4%) HBsAg-positive samples in group I and in three of four (75%) HBsAg-positive samples in group III, whereas the one confirmed HBsAg-negative sample in group III also remained negative for HBV DNA. Amino acid sequences were compared with those specifying the "a" determinant of the wild-type virus, particularly focusing on HBV-S protein variations between positions 110 and 160. Among 11 HBV DNA-positive sera, G145A was detected in 2 samples in group I, with the remaining samples identical to the wild-type virus. These unusual serological profiles may be due to the altered immune response of the host or to HBV variants.

Inhibition of alpha interferon signaling by hepatitis B virus

Alpha interferon (IFN-alpha) and pegylated IFN-alpha (pegIFN-alpha) are used for the treatment of chronic hepatitis B (CHB). Unfortunately, only a minority of patients can be cured. The mechanisms responsible for hepatitis B virus (HBV) resistance to pegIFN-alpha treatment are not known. pegIFN-alpha is also used to treat patients with chronic hepatitis C (CHC). As with chronic hepatitis B, many patients with chronic hepatitis C cannot be cured. In CHC, IFN-alpha signaling has been found to be inhibited by an upregulation of protein phosphatase 2A (PP2A). PP2A inhibits protein arginine methyltransferase 1 (PRMT1), the enzyme that catalyzes the methylation of the important IFN-alpha signal transducer STAT1. Hypomethylated STAT1 is less active because it is bound by its inhibitor, PIAS1. In the present work, we investigated whether similar molecular mechanisms are also responsible for the IFN-alpha resistance found in many patients with chronic hepatitis B. We analyzed the expression of PP2A, the enzymatic activity of PRMT1 (methylation assays), the phosphorylation and methylation of STAT1, the association of STAT1 with PIAS1 (via coimmunoprecipitation assays), the binding of activated STAT1 to interferon-stimulated response elements (via electrophoretic mobility shift assays), and the induction of interferon target genes (via real-time RT-PCR) in human hepatoma cells expressing HBV proteins as well as in liver biopsies from patients with chronic hepatitis B and from controls. We found an increased expression of PP2A and an inhibition of IFN-alpha signaling in cells expressing HBV proteins and in liver biopsies of patients with CHB. The molecular mechanisms involved are similar to those found in chronic hepatitis C.

Diagnostic impact of the genetic variability of the hepatitis B virus surface antigen gene

The genetic variability of hepatitis B virus (HBV) represents a challenge for the sensitivity of immunologic and molecular based assays. Genotyping studies show that the genetic diversity of HBV is very high even in industrialized countries. The analytical sensitivity of HBsAg and anti-HBs assays may be dependent on HBV genotype or subtype and could possibly lead to false negative results in samples with low-level HBsAg. It is possible that the recognition of genotypes E and F may be impaired. Immunoassays based on polyclonal capture antibody show the highest sensitivity for the recognition of recombinant mutants or serum samples harboring mutant forms of HBsAg. However, they do not guarantee full sensitivity, especially for the detection of the G145R mutation and amino acid insertions or substitutions in positions 120-123. Detection of HBsAg needs to be improved by the introduction of new HBsAg assays able to recognize so far described S gene mutants and with a lower detection threshold than current immunoassays in order to detect smallest amounts of HBsAg in low level carriers. There is also a need for more complete epidemiological data on the prevalence of HBsAg mutants especially for G145R and assays for the (differential) screening of mutants need to be developed and evaluated.

HBV virological assessment

Management of hepatitis B virus (HBV) infected patients involves serological diagnosis, quantitation of HBV-DNA and measurement of HBV drug resistance. Different serological markers such as HBsAg, anti-HBs, anti-HBc (total and IgM), HBeAg and anti-HBe are assessed by immunoassays in order to define the infection status. The emergence of surface mutants however is a continuous challenge to design more effective immunoassays. Commercially available quantitative HBV-DNA assays with increased sensitivity and wider linear range give a more accurate estimate of viral replication and contribute decisively in the initiation and the monitoring of the response to HBV therapy. Genotypic drug resistance assays are important diagnostic tools, since the administration of nucleoside/nucleotide analogues to HBV infected patients leads to the development of drug resistance patterns very much dependent on the treatment regimen. Special issues have to be taken into consideration regarding HBV/HIV-1 co-infected patients, since concominant HIV and HBV replication results in higher rates of HBV replication. Current efforts are focused on the standardization of HBV-DNA assays (qualitative and quantitative), of HBV drug resistance assays as well as in the development of new assays and markers that will help in the prognosis and management of HBV infection (quantitative detection of pre-core mutants and HBV ccc-DNA assays).

Evaluation of a new automated assay for hepatitis B surface antigen (HBsAg) detection VIDAS HBsAg Ultra

In a multicenter study a new automated screening assay, VIDAS HBsAg Ultra (long (L) and short (S) incubation protocol (Biomérieux, Marcy l'Etoile, France), was compared to a well established test (AxSYM HBsAg v2, Abbott Diagnostics, Wiesbaden, Germany) for the detection of hepatitis B virus (HBV) surface antigen (HBsAg). A total of 32 seroconversion panels, sera from the chronic phase of infection, dilution series of the WHO standard, S gene mutants (recombinant mutants and diluted and undiluted sera harbouring mutants with single or multiple amino acid (aa) substitutions, n = 40) and isolated anti-HBc positive samples were tested for the evaluation of sensitivity. Sera from HBsAg negative blood donors, pregnant women, hospitalized patients and potentially cross-reactive samples were investigated to determine the specificity of the new assay. The VIDAS HBsAg Ultra (L+S) had a higher sensitivity than the alternative assay for the detection of acute hepatitis B in seroconversion panels. The mean time of the diagnostic window was shortened with the VIDAS HBsAg Ultra (L) and (S) in comparison with the AxSYM HBsAg v2 by 1.06 and 0.66 days, respectively. The VIDAS HBsAg Ultra (L) did not detect one diluted sample out of six bearing the single aa G145R substitution, and two out of 12 diluted samples harbouring multiple aa substitutions. The analytical sensitivity of the assays varied from one surface mutant to another. While no false positive results were obtained with the VIDAS HBsAg Ultra (L+S) among potentially interfering samples, four false positives were detected with the AxSYM HBsAg v2. The respective values for sensitivity for the VIDAS HBsAg Ultra (L), (S) and the AxSYM HBsAg v2 were 99.07%, 97.87% and 94.14%. The specificities were 100% (VIDAS HBsAg Ultra L and S) and 99.6% (AxSYM HBsAg v2). In conclusion, the VIDAS HBsAg Ultra is highly sensitive and specific and represents an improvement for the detection of HBsAg in routine diagnostic laboratories.

Rapid and sensitive HBsAg immunoassay based on fluorescent nanoparticle labels and time-resolved detection

The detection of hepatitis B virus in blood specimens is carried out commonly by measuring surface antigen (HBsAg) levels with assays designed for various random access immunoanalysers or rapid near-patient testing. These methods leave much to be desired in performance or throughput. The aim of this study was to develop a nanoparticle label-based rapid and sensitive HBsAg immunoassay and evaluate its performance compared to a well-established reference immunoassay (Enzygnost HBsAg 5.0). The assay developed is based on kinetic format and relies on one-step two-site antibody-antigen interaction. Europium(III)-chelate-doped nanoparticles and microtiter wells were coated with anti-HBsAg monoclonal antibodies specific for discrete epitopes. The adaptation of nanoparticle labels for quantitative HBsAg detection showed improved sensitivity (LLD: 0.028 ng/ml) and dynamics (up to 1000 ng/ml) with reasonably low coefficients of variation (concentration-CV%s 2.8-21.9%). Furthermore, concurrent sample runs with the ELISA reference method showed 100% agreement. The time required for the assay was only 10 min facilitating a rapid and convenient method for hepatitis B screening.

Recent developments in the diagnosis and monitoring of HBV infection and role of the genetic variability of the S gene

Recent developments in the laboratory diagnosis of hepatitis B virus infection include the optimization of key serologic markers, including hepatitis B virus surface antigen and antihepatitis B virus core antibody, as well as the development of automated nucleic acid amplification assays. There is still a lack of standardization for nucleic acid amplification assays that are used for the monitoring of antiviral therapy and follow-up of chronic infection and the clinical significance of hepatitis B virus DNA levels need to be clarified. Although highly sensitive automated nucleic acid amplification assays for blood donor screening are available, their implementation is still subject to discussion and certain countries rejected hepatitis B virus DNA testing for blood donation due to poor cost effectiveness. Genetic variability of hepatitis B virus constitutes a major challenge for diagnosis of hepatitis B virus infection, particularly with regard to hepatitis B virus surface antigen detection, antihepatitis B virus surface antigen quantification and nucleic acid amplification assays. The performances of hepatitis B virus surface antigen enzyme immunoassays in regard to genotype and surface antigen variability need to be further improved. Polyclonal antibody-based hepatitis B virus surface antigen enzyme immunoassays, although they cannot guarantee 100% sensitivity, demonstrate superior S gene mutant recognition to assays using monoclonal capture and tracer antibodies. Isolated antihepatitis B virus core reactivity is an unusual but frequent result, which requires a test algorithm for resolution and hepatitis B virus DNA detection with sensitive nucleic acid amplification assays in order to exclude occult hepatitis B virus infection.

Genetic variability of the S gene of hepatitis B virus: clinical and diagnostic impact

The genetic variability of hepatitis B virus (HBV) represents a challenge for the sensitivity of immunologic and molecular based assays. Based on sequence divergence in the entire genome of >8%, HBV genomes have been classified into eight groups designated A to H. The genotypes of HBV have distinct geographical distributions. Although preliminary clinical studies seem to indicate that there is an association between HBV genotype and natural history of infection and response to antiviral therapy, further evaluations on larger collectives of patients are necessary to give a clearer picture of the subject. The analytical sensitivity of HBsAg and anti-HBs assays may be dependent on HBV genotype or subtype. The influence of genotypic variability on the sensitivity of nucleic acid amplification tests (NAT) has so far been poorly investigated. Preliminary results show that new real-time NAT detect genotypes A to G with an equal sensitivity. Different mechanisms intervening at the translational or post-translational level, including conformational changes, hydrophobic changes, insertion of basic residues and reduced synthesis or secretion of HBsAg may account solely or in conjunction for escape mutations to the immune response and to detection in HBsAg immunassays. The clinical significance of S-gene mutants, needs in analogy to that of HBV genotypes, to be further investigated. HBV mutants are stable over time and can be transmitted horizontally or vertically. The sensitivity of HBsAg assays for mutant detection is continuously improved. Immunoassays based on polyclonal capture antibody show the highest sensitivity for the recognition of recombinant mutants or serum samples harboring mutant forms of HBsAg. However, they do not guarantee full sensitivity. Detection of HBsAg needs to be improved by the introduction of new HBsAg assays able to recognize so far described S-gene mutants and with a lower detection threshold than current immunoassays in order to detect smallest amounts of HBsAg in low level carriers. There is also a need for more complete epidemiological data on the prevalence of HBsAg mutants and strategies for the (differential) screening of mutants need to be developed and evaluated.

Detection of an acute asymptomatic HBsAg negative hepatitis B virus infection in a blood donor by HBV DNA testing

The issue of HBV DNA screening on blood donations is controversially discussed since the economic impact of post-transfusion hepatitis B is expected to be relatively low. We report on a case of HBsAg negative unapparent acute HBV infection, which was detected by HBV NAT testing on 96-member maxi-pools with a commercially available NAT assay, which has a detection threshold of 3 IU/mL of plasma. The presence of an HBsAg escape mutant could be excluded by sequencing the amplified DNA. Follow-up testing showed the presence of an acute HBV infection (anti-HBc-IgM positive) and finally anti-HBs seroconversion. Although the reduction of the diagnostic window with NAT screening on maxi-pools may be relatively low, it may help to improve the residual risk of blood donation, especially in asymptomatic HBV infection, where the HBsAg positive period may be very short and low levels of circulating surface antigen are present. It would also permit to detect occult HBV infection in chronic carriers who are HBsAg negative. Since the viral load in chronic isolated anti-HBc positive carriers is low, there is a potential risk for failure of HBV DNA detection with pool-PCR in blood donors. Anti-HBc screening would reduce the residual risk.

A rapid immunochromatographic assay for hepatitis B virus screening

Simple, rapid and accurate assays for hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) are helpful for clinical diagnosis and field epidemiological surveys. A commercially developed, rapid immunochromatographic test for simultaneous detection of HBsAg and HBeAg was evaluated using a total of 2463 selected samples (827 frozen sera, 1011 fresh sera, and 625 whole blood samples). Results of the rapid test were compared with standard enzyme immunoassay (EIA) methods for HBsAg and HBeAg detection. The accuracy of the rapid test was excellent and was similar for frozen sera, fresh sera and whole blood. The overall sensitivity and specificity for the detection of HBsAg were 95 and 100%, and the corresponding positive and negative predictive values were 100 and 99.7%, respectively. The sensitivity and specificity for the detection of HBeAg were slightly less than that for HBsAg, and were 80 and 98%, with positive and negative predictive values of 91 and 94%, respectively. Thus, compared with the EIA method, the rapid test was highly sensitive and accurate for the detection of HBsAg although somewhat less sensitive and specific for detection of HBeAg. Because of its speed, simplicity and flexibility, the rapid test is ideally suited for HBsAg and HBeAg screening in population-based epidemiological studies and in low risk populations, particularly in regions of the world where hepatitis B is endemic.

Evaluation of two new automated assays for hepatitis B virus surface antigen (HBsAg) detection: IMMULITE HBsAg and IMMULITE 2000 HBsAg

In recent years the diagnostic industry has developed new automated immunoassays for the qualitative detection of hepatitis B virus (HBV) surface antigen (HBsAg) in serum and plasma samples that are performed on analyzers that permit a high-speed throughput, random access, and primary tube sampling. The aim of the present study was the evaluation of two new automated HBsAg screening assays, IMMULITE HBsAg and IMMULITE 2000 HBsAg, from Diagnostic Products Corporation. The new HBsAg assays were compared to well-established tests (Auszyme Monoclonal [overnight incubation, version B], IMx HBsAg, AxSYM HBsAg, and Prism HBsAg [all from Abbott] and Elecsys HBsAg [Roche Diagnostics]). In the evaluation were included seroconversion panels, sera from the acute and chronic phases of infection, dilution series of various HBsAg standards, HBV subtypes and S gene mutants. To challenge the specificity of the new assays, sera from HBsAg-negative blood donors, pregnant women, and dialysis and hospitalized patients and potentially cross-reactive samples were investigated. IMMULITE HBsAg and IMMULITE 2000 HBsAg, although not as sensitive as the Elecsys HBsAg assay, were equivalent to the AxSYM HBsAg assay and showed a higher sensitivity than the Auszyme Monoclonal B and IMx HBsAg systems for detection of acute infection in seroconversion panels. The specificities (100%) of both IMMULITE assays on unselected blood donors and potentially interfering samples were comparable to those of the alternative assays after repeated testing. In conclusion, the new IMMULITE HBsAg and IMMULITE 2000 HBsAg assays show a good sensitivity for HBsAg detection compared to other well-established tests. The specificity on repeatedly tested samples was equivalent to that of the alternative assays. The rapid turnaround time, primary tube sampling, and on-board dilution make it an interesting assay system for clinical laboratory diagnosis.

High-throughput HBV DNA and HCV RNA detection system using a nucleic acid purification robot and real-time detection PCR: its application to analysis of posttransfusion hepatitis

BACKGROUND

A high-throughput detection system was developed for HBV DNA and HCV RNA.

METHODS

A combination of real-time detection PCR using an automated system (PRISM 7700, PE Biosystems, Foster City, CA) and automatic viral nucleic acid extraction (BioRobot 9604, Qiagen, Hilden, Germany) was used as the high-throughput detection system. An internal control for HBV DNA detection was also developed.

RESULTS

Testing of 96 samples for HBV and HCV was completed within 5 hours. The sensitivity of this system almost equals that of the manual method using nested PCR. The addition of an internal control for HBV detection did not affect the sensitivity of the method and confirmed the accuracy of results. It was possible to quantify HBV in HBV+ samples that contain more than 500 genome equivalents per mL. We started using this system from June 1999 for testing stored donor and patient samples to analyze cases of posttransfusion hepatitis and identified three HBV+ donations that were implicated in posttransfusion hepatitis B.

CONCLUSION

The high-throughput detection system is a useful tool for HBV DNA and HCV RNA detection because it enables rapid and reliable testing of a large number of samples.