The Role of Hepatitis C Virus Core Antigen Testing in the Era of Direct Acting Antiviral Therapies: What We Can Learn from the Protease Inhibitors

Diagnostic performance of hepatitis C core antigen assay to identify active infections: A systematic review and meta-analysis

Hepatitis C virus (HCV) core antigen (HCVcAg) assay is an alternative for diagnosing HCV infection in a single step. This meta-analysis aimed to evaluate the Abbott ARCHITECT HCV Ag assay's diagnostic performance (validity and utility) for diagnosing active hepatitis C. PubMed, EMBASE, Scopus, Web of Science, and Cochrane Library were searched until 10 January 2023. The protocol was registered at the prospective international register of systematic reviews (PROSPERO: CRD42022337191). Abbott ARCHITECT HCV Ag assay was the test for evaluation, and nucleic acid amplification tests with a cut-off ≤50 IU/mL were the gold standard. Statistical analysis was performed using STATA with the MIDAS module and random-effects models. The bivariate analysis was conducted on 46 studies (18,116 samples). The pooled sensitivity was 0.96 (95% CI = 0.94-0.97), specificity 0.99 (95% CI = 0.99-1.00), positive likelihood ratio 141.81 (95% CI = 72.39-277.79), and negative likelihood ratio 0.04 (95% CI = 0.03-0.06). The area under the summary receiver operating characteristic curve was 1.00 (95% CI = 0.34-1.00). For active hepatitis C prevalence values of 0.1%-15%, the probability that a positive test was a true positive was 12%-96%, respectively, indicating that a confirmatory test should be necessary, particularly with a prevalence ≤5%. However, the probability that a negative test was a false negative was close to zero, indicating the absence of HCV infection. The validity (accuracy) of the Abbott ARCHITECT HCV Ag assay for screening active HCV infection in serum/plasma samples was excellent. Although the HCVcAg assay showed limited diagnostic utility in low prevalence settings (≤1%), it might help diagnose hepatitis C in high prevalence scenarios (≥5%).

Meta-analysis: diagnostic accuracy of hepatitis C core antigen detection during therapy with direct-acting antivirals

BACKGROUND

Treatment of hepatitis C virus (HCV) infection with direct-acting antivirals (DAAs) is monitored by assessing plasma HCV-RNA load. However, detection of HCV core antigen (HCVcAg) may be an alternative.

AIM

To evaluate the diagnostic performance of the HCVcAg assay to monitor the efficacy of DAAs in HCV-infected patients METHODS: We performed searches in multiple electronic databases until 6 July 2022, of studies evaluating the HCVcAg detection in plasma or serum compared with the HCV-RNA test (gold standard). We calculated pooled measurement at 2 and 4 weeks of treatment, and at end-of-treatment (EOT), as well as sustained virological response (SVR; 12 weeks after EOT).

RESULTS

We selected 16 studies from 2016 to 2022, with 3237 patients and 8958 samples. Overall, the diagnostic performance and clinical utility of the HCVcAg assay were poor at week 2 (sensitivity = 0.40, specificity = 0.96, positive likelihood ratio (PLR) = 9.16, negative likelihood ratio (NLR) = 0.63, and area under the summary receiver operating curve (SROC) = 0.57), fair at week 4 (sensitivity = 0.30, specificity = 0.90, PLR = 3.18, NLR = 0.77, and AUC = 0.79), acceptable at EOT (sensitivity = 0.40, specificity =0.98, PLR = 16.54, NLR = 0.62, and AUC = 0.97) and excellent for SVR (sensitivity = 0.94, specificity = 0.99, PLR = 107.54, NLR = 0.06, and AUC = 0.99).

CONCLUSIONS

The HCVcAg assay may be helpful for monitoring the efficacy of HCV treatment with DAAs in HCV-infected patients at EOT and for documenting SVR, but not at weeks 2 and 4 of treatment due to poor diagnostic performance.

Resistant-Associated Substitutions Do Not Affect HCV RNA and HCV Core Antigen Clearance During Direct-Acting Antiviral Agent Treatment in a Real-World Setting

Background

Since oral direct-acting antiviral agents (DAAs) became available, the global hepatitis C treatment situation has undergone tremendous changes. However there are still many issues worthy of attention in treatment.

Methods

We selected 53 HCV-infected patients who were treated and followed up in the Peking University First Hospital from December 2017 to January 2021 to detect the RASs in HCV. Pearson correlation analysis was used to analyze HCV RNA and HCV cAg, the Fisher exact test and chi-square test was used to compare the effects of RASs on the rate of decline of HCV RNA and HCV core antigen (cAg) during DAA treatment.

Results

The RASs and its prevalence on the NS3 are mainly Y56F 2.56% (1/39), Q80K 23.08% (9/39), S122G 71.79% (28/39), and V170I 38.46% (15/39). On the NS5A were R30Q 10.53% (4/38), P32A 5.26% (2/38), P58S 2.63% (1/39), and Y93H 21.05% (8/38). On NS5B were C316N 71.05% (27/38), C451H 2.63% (1/38), and I585C 2.63% (1/38). There was no significant correlation between the RASs (Y93H, V179I, Q80K, S122G, C316N) and HCV genotype (p > 0.05). The baseline serum HCV RNA and HCV cAg had a significant medium-degree correlation (r = 0.601, p = 0.002). After 1 week of DAA treatment was weak correlation (r = 0.413, p = 0.032). Q80K, S122G, V170I, Y93H, and C316N had no effect on the clearance of HCV RNA and HCV cAg within the first week of DAA treatment (p>0.05).

Conclusion

The HCV genotype may have a limited impact on the presence of the five RASs (Y93H, V179I, Q80K, S122G, and C316N) as shown in this study. HCV RNA and HCV cAg have a correlation, especially at baseline is the highest; the appearance of some RASs has no effect on DAA treatment in most chronic hepatitis C patients.

Performance of HCV Antigen Testing for the Diagnosis and Monitoring of Antiviral Treatment: A Systematic Review and Meta-Analysis

BACKGROUND AND AIMS

Active hepatitis C virus (HCV) infection is based on the detection of HCV RNA that it is effective but presents high cost and the need to hire trained personnel. This systematic review and meta-analysis is aimed at evaluating the diagnostic accuracy of HCV Ag testing to identify HCV cases and to monitor antiviral treatment including DAA treatment.

METHODS

The studies were identified through a search in PubMed, Lilacs, and Scopus from 1990 through March 31, 2020. Cohort, cross-sectional, and randomized controlled trials were included. Two independent reviewers extracted data and assessed quality using an adapted Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool. Our primary outcome was to determine the accuracy of HCV Ag detection for the diagnosis, which we estimated using random-effects meta-analysis.

RESULTS

Of 3,062 articles identified, 54 met our eligibility criteria. The studies described cohorts from 20 countries, including 14,286 individuals with chronic HCV individuals. Studies for ECLIA technology demonstrated highest quality compared to studies that used ELISA. The pooled sensitivity and specificity (95% CI) for HCV Ag detection of active HCV infection were 98.82% (95%CI = 98.04%; 99.30%) and 98.95% (95%CI = 97.84%; 99.49%), respectively. High concordance was found between HCV Ag testing and HCV RNA detection 89.7% and 95% to evaluate antiviral treatment.

CONCLUSIONS

According to our findings, HCV Ag testing could be useful to identify HCV active cases in low-resource areas. For antiviral treatment, HCV Ag testing will be useful at the end of treatment.

Hepatitis C Virus Core Antigen as an Alternative to RNA in the Assessment of Response to Treatment with Direct-acting Oral Antivirals

Background: Affordable and effective diagnostic and treatment monitoring algorithms are urgently needed to achieve the global elimination of hepatitis C virus (HCV) infection. Methods: A total of 274 patients were treated with direct-acting antivirals (DAAs) in the Spanish Hospital of Albacete between 2004 and 2020. This study compared the enzyme-immunoassay technique for HCV core antigen (HCVcAg) with the determination of RNA of HCV (HCV RNA) by polymerase chain reaction (PCR) in monitoring treatment with DAA, setting the lower limit of detection of HCVcAg < 3 fmol/L and RNA < 10 IU/mL. In all cases, the P value of differences associated with the contrast test was less than or equal to 0.05. Results: We evaluated the viral loads of our patients before treatment, during their treatment, and after its completion. The HCV RNA quantification at diagnosis was 2309327 IU/mL. The mean HCVcAg load was 5972 fmol/L. There was a strong correlation between HCVcAg levels and RNA levels with a Spearman rho of 0.832 (P < 0.01). The HCVcAg sensitivity at diagnosis was 99%, but the specificity could not be calculated because there were no true negatives or false positives at this point. Twelve weeks after treatment, in patients with treatment failure, we obtained a mean of 19084 IU/mL for RNA, while for HCVcAg, the mean was 103 fmol/L. At this time point, we also found a strong correlation between HCVcAg levels and HCV RNA levels with a Spearman rho of 0.775 (P < 0.01). Finally, the virological cure was achieved in 99% of our patients. The results for sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 100%, 99.87%, 86.33%, and 100%, respectively. Conclusions: HCVcAg determination is an excellent alternative to HCV RNA in the assessment of treatment response. This is particularly relevant in lower- and middle-income countries and resource-limited settings where the high cost of labor, equipment, and reagents can prohibit molecular testing.

Current position of viral load versus hepatitis C core antigen testing

Quantification of hepatitis C virus (HCV) RNA (viral load) is the most widely used marker to diagnose and confirm active HCV infection. The HCV core antigen forms part of the internal structure of the virus and, like HCV RNA, its detection also indicates viral replication and presents certain advantages over viral load testing such as its lower cost, the greater stability of the target, the possibility of working with the same primary tube as that used for HCV serology, and the rapidity of obtaining results, since there is no need to work in batches, unlike the situation with most viral load platforms. Although the core antigen has lower analytical sensitivity than HCV RNA for the detection of low viremia levels, several studies and guidelines have already shown their utility in the identification of patients with active HCV infection. This article summarises current platforms for viral load determination, including point-of-care systems, and also reviews the indications attributed to this marker by the main HCV treatment guidelines. The article also reviews the characteristics of HCV core antigen, the available platforms for its determination, its correlation with viral load determination, and the indications for this marker in the distinct guidelines.

HCV core antigen plays an important role in the fight against HCV as an alternative to HCV-RNA detection

Objective

To discuss the clinical significance of HCV‐cAg testing in the diagnosis, activity determination, and monitoring of therapeutic effectiveness of HCV infection and its advantages compared with HCV‐RNA and anti‐HCV antibodies detection.

Methods

By summarizing the published literature, the advantages and significance of HCV core antigen detection were sought.

Results

The expression of HCV‐cAg is highly consistent with that of HCV‐RNA, but compared with HCV‐RNA, detection of HCV‐cAg is easy to operate, time saving, and low cost. HCV‐cAg can be detected within 12~15 days after infection, and the window period can be shortened by5~7 weeks. HCV‐cAg is a serological indicator of virus replication, which can distinguish previous infection of HCV or current infection. HCV‐cAg detection is more suitable for immunocompromised, hemodialysis, organ transplant patients. HCV‐cAg also can be used to monitor antiviral efficacy and predict sustained virological response (SVR).

Conclusion

HCV core antigen has similar clinical sensitivity to NAT and can be used as a substitute for HCV‐RNA in the diagnosis of virus infection. Combined detection of HCV‐cAg and antibody serology can help doctors detect HCV infection earlier, accurately diagnose different stages of HCV infection, and evaluate the therapeutic effect of antiviral drugs, which are beneficial in the prevention and treatment of hepatitis C.

Hepatitis C core antigen: a simple predictive marker for treatment response to the new direct-acting antiviral drugs in chronic HCV Egyptian patients

Background

Successful eradication of hepatitis C virus (HCV) has great impact on the prognosis of HCV-related complications and the associated mortality. The development of the new direct-acting antiviral drugs (DAAs) has revolutionized the treatment of HCV infection. HCV core antigen (HCVcAg) is a recently developed marker that displayed a good correlation with HCV RNA assays. Our main objectives were to correlate between serum levels of HCVcAg and HCV RNA loads in chronic HCV patients as well as to explore the potential value of HCVcAg assay in predicting treatment response to the new DAAs. The study enrolled a total of 280 chronic HCV-infected patients scheduled to start the new regimen for treatment of chronic HCV by all-oral, interferon-free DAAs. According to the viral load, the studied individuals were arranged into three groups corresponding to mild, moderate, and sever viremia. Serum level of HCVcAg was determined by ELISA technique and HCV RNA viral loads were quantified using the real-time PCR system. The assays were performed three times for all participants: prior to initiation of treatment, at the end of treatment (week 12), and 3 months post-treatment cessation (week 24).

Results

A statistically significant difference between HCV RNA and HCVcAg baseline levels among different viremia groups was detected (P < 0.001). There was a significant positive correlation between HCV RNA and HCVcAg baseline values among all the studied cases (P < 0.05) with a correlation coefficient of 0.752, 0.976, and 1.00 respectively for mild, moderate, and severe viremia groups. 92.9% (260/280) of the studied patients achieved sustained virologic response, 3.6% (10/280) were non-responders, and 3.6% (10/280) had recurrent viremia/relapse as regards RT-PCR results.

Conclusion

HCVcAg is a promising alternative to HCV RNA assay. The ELISAs for HCVcAg proved excellent correlations with HCV RNA levels. Moreover, HCVcAg can be introduced as a simple and highly specific tool for monitoring the new DAA regimens particularly in low-resource settings.

Clinical utility of hepatitis C virus core antigen assay in the monitoring of direct-acting antivirals for chronic hepatitis C

BACKGROUND

Hepatitis C virus core antigen (HCV Ag) assay has been proposed as a more economical alternative to HCV RNA detection. This study aimed to investigate the clinical utility of HCV Ag assay in the monitoring of direct-acting antivirals (DAAs) for chronic hepatitis C patients.

METHODS

We analyzed serum samples from 110 patients treated with paritaprevir/ritonavir, ombitasvir, and dasabuvir (PrOD) with or without ribavirin. The levels for both HCV Ag and HCV RNA assessed by COBAS TaqMan HCV (CTM) Test or Abbott RealTime HCV (ART) assay were evaluated at baseline, week 2, 4, and 12 during treatment and 12 weeks after completion.

RESULTS

Baseline HCV Ag levels showed good correlations with HCV viral load (r = 0.879; p<0.001); whereas the correlation was slightly stronger with CTM test than with ART assay (p = 0.074). The concordance of HCV Ag and HCV RNA undetectability was significantly better in CTM test than in ART assay at week 2 (p = 0.003) and week 4 (p = 0.003). A sustained viral response 12 weeks off therapy (SVR12) was achieved in 108 patients (98%); the HCV Ag assay identified 99% of these patients. Both undetectability of serum HCV Ag and HCV RNA had high positive predictive value at week 2 (98% vs. 100%) and at week 4 (97% vs. 99%) in predicting SVR12.

CONCLUSIONS

HCV Ag assay may be a feasible alternative to HCV RNA for the determination of SVR12 in patients treated with DAAs.

Correlation analysis of hepatitis C virus core antigen and low viral loads: Can core antigen replace nucleic acid test?

Value of hepatitis C virus (HCV) core antigen (cAg) test has been controversy in patients with low HCV loads for its lower sensitivity. We assessed correlation between HCV-cAg and HCV RNA in serum samples with low viral loads and analyzed the performance of HCV-cAg assay in determining diagnosis and treatment outcomes in chronic hepatitis C patients. Both HCV RNA and HCV-cAg were detected for 2298 serum samples. Correlation analysis was performed between the two tests. Receiver operating characteristics (ROC) curve was used to assess value of HCV-cAg test in determining diagnosis and response outcomes at the different HCV RNA thresholds. The two tests were correlated very well, and moreover, correlation in the low viral load group was higher than that in the high viral load group (r value: 0.901 and 0.517). Positive agreement of HCV-cAg ≥ 3 fmol/L was as high as 97.0% for HCV RNA ≥ 1000 IU/mL, and its negative agreement for HCV RNA < 15 IU/mL was up to 98.9% in all samples. Area under ROCs ranged from 0.939 to 0.992, regardless of HCV RNA thresholds. When lower limit of detection of HCV RNA was 15, 100 or 1000 IU/mL, positive predictive value of HCV-cAg was 96.8%, 98.8% or 92.4%, and its negative predictive value was 87.0%, 89.9% or 98.3%, respectively, on the basis of different cutoff values. High-sensitivity HCV-cAg detection may likely replace HCV RNA to confirm the existence of HCV and to guide the treatment of chronic HCV infection.

Implications of grey zone results for routine hepatitis C virus screening with the ARCHITECT HCV-Ag assay

AIMS

Hepatitis C virus antigen (HCV-Ag) detection requires retesting for samples with grey zone results (GzR), adding cost and time and decreasing reliability. Our aim in this study was to evaluate the frequency and significance of GzR during the use of the automated Architect HCV-Ag assay in routine clinical practice.

METHODS AND RESULTS

We studied HCV-Ag levels in 952 serum samples using the ARCHITECT HCV-Ag assay. GzR were detected in 33 samples; 25 were reactive on retesting and 19 were anti-HCV positive. Seventeen of these 19 samples were tested for HCV-RNA and were all reactive (viral loads <10⁴  IU ml^-1 ). The remaining six samples were anti-HCV nonreactive and had undetectable HCV-RNA. Eight GzR samples were nonreactive on retesting, seven were anti-HCV nonreactive (three underwent HCV-RNA quantification and were all nonreactive), and one was anti-HCV reactive (HCV-RNA nonreactive). No significant differences were found on comparing HCV-Ag values.

CONCLUSIONS

Grey zone results found to be negative on retesting do not need additional technique testing, except in donor screening scenarios, where the use of molecular methods would be advisable.

SIGNIFICANCE AND IMPACT OF THE STUDY

 The proposed diagnostic algorithm confirms that, eventhough GzR occur, hepatitis C virus antigen is a robust alternative to HCV-RNA detection in the active detection of infections.

Quantitative measurement of HCV core antigen for management of interferon-free therapy in HCV-infected patients

BACKGROUND

According to current recommendations diagnosis and management of HCV infection need detection and quantification of nucleic acids. In the era of direct-acting antivirals (DAA) it is essential to develop an inexpensive and simple method replacing polymerase chain reaction. Since there is no available data on HCV core antigen (HCVcAg) versus HCV RNA kinetics in the early phase of treatment with DAA, we carried out this study to evaluate the possible application of HCVcAg quantitative measurement for management of HCV infection.

METHODS

33 patients with HCV infection were enrolled and treated with either ombitasvir/paritaprevir/ritonavir ± dasabuvir ± ribavirin (OBV/PRV/r±DSV±RBV) or ledipasvir/sofosbuvir (LDV/SOF). Samples for quantitative HCV RNA and HCVcAg measurement were collected at the baseline, after 1, 7, 28 days and at the end of treatment, and then after 12 and 24 weeks of post-treatment follow-up.

RESULTS

There was positive correlation between HCVcAg and HCV RNA levels at the baseline and after 1 day of treatment. Mean HCVcAg concentration declined faster than HCV RNA levels during the treatment phase. At week 4 HCV RNA was undetectable in 24, whereas HCVcAg in 28 patients. At the end of treatment and after 12 weeks of follow-up all patients were undetectable for both HCV RNA and HCVcAg.

CONCLUSIONS

HCVcAg concentration and its early on-treatment testing can predict virological response. Simple testing procedures and significantly lower cost compared to HCV RNA testing support possible replacement of the viral load measurement in management of the majority of HCV-infected patients.

HCV core antigen comes of age: a new opportunity for the diagnosis of hepatitis C virus infection

The diagnosis of hepatitis C virus (HCV) infection has been traditionally based on the detection of the host antibody response. Although antibody assays are available in different formats and are fairly accurate, they cannot distinguish between an ongoing infection with HCV replicative activity and a past infection where HCV has been cleared, spontaneously or after a successful therapy. As a chronic infection is mostly asymptomatic until the late clinical stages, there is a compelling need to detect active HCV infection by simple and reproducible methods. On this purpose, the clinical guidelines have suggested to search for the HCV ribonucleic acid (HCV-RNA) after anti-HCV has been detected, but this second step carries several limitations especially for population screening. The availability of fast and automated serological assays for the hepatitis C core antigen (HCVAg) has prompted an update of the guidelines that now encompass the use of HCVAg as a practical alternative to HCV-RNA, both for screening and monitoring purposes. In this paper, we summarize the features, benefits and limitations of HCVAg testing and provide an updated compendium of the evidences on its clinical utility and on the indications for use.

Clinical Evaluation of a Newly Developed Chemiluminescent Enzyme Immunoassay for Hepatitis C Virus Core Antigen in Japan

An advanced and fully automated chemiluminescent enzyme immunoassay for the hepatitis C virus core antigen (HCVcAg) was recently developed in Japan. We aimed to evaluate its clinical utility. The new Fujirebio assay (Lumipulse Presto HCVcAg [LP-Presto]) was compared with 2 conventional assays (Lumipulse Ortho HCVcAg [LP-Ortho] and Abbott's Architect HCVcAg). Basic assessments of LP-Presto (reproducibility, stability, range of quantitation, and specificity) were performed on 220 frozen sera (83 positive and 137 negative by LP-Ortho) and 206 fresh sera (all negative by LP-Ortho). Correlation analysis was performed and the rates of concordance for each assay were determined. Additionally, the frozen sera of 42 hyperimmunoglobulinemia patients, including 3 unmeasurable by LP-Ortho, were tested by LP-Presto. All the basic assessments of LP-Presto were consistent with the results of LP-Ortho and Architect. The concordance rate between LP-Presto and LP-Ortho for the 220 frozen sera was 99.5% (219/220), and that between LP-Presto and Architect was 99.1% (218/220). LP-Presto (HCVcAg cut-off value; 20 fmol/L) was fully consistent with LP-Ortho (100%), which found 343 sera negative for HCVcAg. All 42 hyperimmunoglobulinemic sera were measurable using LP-Presto. In conclusion, the performance of LP-Presto was rapid and reliable, and nonspecific test results due to hyperimmunoglobulinemia were reduced when LP-Presto was used. Therefore, LP-Presto is a high-quality HCVcAg assay that shows promising applications.

HCV core antigen is an alternative marker to HCV RNA for evaluating active HCV infection: implications for improved diagnostic option in an era of affordable DAAs

The core antigen of the hepatitis C virus (HCV Ag) presents an alternative marker to HCV RNA when screening patients for HCV viremia. This study sought to evaluate the utility of HCV Ag as a marker to assess active HCV infection in individuals residing in an HCV-endemic area. From 298 HCV-seropositive individuals evaluated for the presence of anti-HCV antibody, HCV Ag and HCV RNA, anti-HCV antibody was detected in 252 individuals (signal-to-cutoff ratios ≥5), HCV RNA was detected in 222 individuals (88%), and HCV Ag was reactive (≥3 fmol/L) in 220 individuals (87%). HCV genotype 1, 3, and 6 were identified. HCV Ag significantly correlated with HCV RNA irrespective of HCV genotype and/or HBV co-infection (log HCV RNA = 2.67 + 0.95 [log HCV Ag], R² = 0.890, p < 0.001). To predict HCV viremia (HCV Ag ≥ 3 fmol/L), the accuracy, sensitivity, specificity, positive predictive value, and negative predictive value were 99%, 99%, 100%, 100% and 97%, respectively. We concluded that HCV Ag was a good surrogate marker for HCV RNA and could be used to diagnose active HCV infection in a resource-limited setting. As a result, a cost-effective strategy for screening and identifying active HCV carriers using HCV Ag detection would enable more patients access to efficacious and increasingly affordable direct-acting antivirals (DAAs) for the treatment of HCV infection.

Hepatitis C virus core antigen: A simplified treatment monitoring tool, including for post-treatment relapse

BACKGROUND

Simple, affordable diagnostic tools are essential to facilitate global hepatitis C virus (HCV) elimination efforts.

OBJECTIVES

This study evaluated the clinical performance of core antigen (HCVcAg) assay from plasma samples to monitor HCV treatment efficacy and HCV viral recurrence.

STUDY DESIGN

Plasma samples from a study of response-guided pegylated-interferon/ribavirin therapy for people who inject drugs with chronic HCV genotype 2/3 infection were assessed for HCV RNA (AmpliPrep/COBAS Taqman assay, Roche) and HCVcAg (ARCHITECT HCV Ag, Abbott Diagnostics) during and after therapy. The sensitivity and specificity of the HCVcAg assay was compared to the HCV RNA assay (gold standard).

RESULTS

A total of 335 samples from 92 enrolled participants were assessed (mean 4 time-points per participant). At baseline, end of treatment response (ETR) and sustained virological response (SVR) visits, the sensitivity of the HCVcAg assay with quantifiable HCV RNA threshold was 94% (95% CI: 88%, 98%), 56% (21%, 86%) and 100%, respectively. The specificity was between 98 to 100% for all time-points assessed. HCVcAg accurately detected all six participants with viral recurrence, demonstrating 100% sensitivity and specificity. One participant with detectable (non-quantifiable) HCV RNA and non-reactive HCVcAg at SVR12 subsequently cleared HCV RNA at SVR24.

CONCLUSIONS

HCVcAg demonstrated high sensitivity and specificity for detection of pre-treatment and post-treatment viraemia. This study indicates that confirmation of active HCV infection, including recurrent viraemia, by HCVcAg is possible. Reduced on-treatment sensitivity of HCVcAg may be a clinical advantage given the moves toward simplification of monitoring schedules.