HCV infection is a serious public health issue. Early detection and treatment are imperative to prevent its transmission. Limitations of anti-HCV and HCV RNA detection have restricted their applications in clinical practice [16].
HCVcAg has been proposed as an indirect marker of viral replication [16]. Recently, many assays have been developed for both qualitative and quantitative HCVcAg estimation, such as enzyme immunoassays (EIAs) or chemiluminescent immunoassays with an excellent correlation between HCVcAg concentrations and HCV RNA levels. These quantitative HCVcAg assays became promising alternatives to HCV nucleic acid-based techniques [17, 18].
In the current study, 280 patients with chronic HCV infection have been enrolled and arranged into mild, moderate, and severe viremia groups according to their HCV viral load. All studied individuals were prescribed the new regimen of anti-HCV treatment which included the new oral, interferon-free DAAs. The main targets were to correlate between baseline levels of both HCVcAg and HCV viremic load and to assess the utility of HCVcAg testing in the era of DAAs.
The recorded data denoted a highly significant statistical difference between the baseline values of both HCV RNA and HCVcAg among different viremia groups (P < 0.001). Furthermore, a significant positive correlation was detected between HCV RNA and HCVcAg baseline levels for all the studied cases (P < 0.05) (correlation coefficient; r = 0.752 for mild viremia, r = 0.976 for moderate viremia, and r = 1.00 for severe viremia). These finding agreed with previous reports by Soliman et al., Park et al., and Kim et al. [15, 19, 20] who confirmed excellent correlation to HCV RNA levels and that the kinetics of HCVcAg and viremia were almost similar. Thong et al. also postulated that in the overall cohort, HCVcAg levels significantly correlated with the corresponding HCV RNA levels (r = 0.889, P < 0.001). The authors recommended HCVcAg testing to be used as an alternative to HCV RNA assays in resource-limited settings [21].
Other previous studies involving other HCV genotypes demonstrated that detection of HCVcAg in serum or plasma is useful as an indirect marker of HCV replication due to the excellent correlation between HCVcAg and HCV RNA concentrations. In addition, HCVcAg assays, which are easier to perform than reverse transcription-PCR, also save time and are less expensive. HCVcAg is used currently to monitor patients undergoing antiviral therapy and to determine the clinical efficacy of such treatment [22,23,24].
Being closely related to HCV RNA as proved in current results, the present study involved analytical data that may support the use of HCVcAg as a prognostic marker for disease activity among HCV-infected patients and consequently to be implemented in clinical practice for the follow-up of treatment response. At a cutoff point of 1.765 Peiu/ml, HCVcAg was able to differentiate between mild and moderate viremia with sensitivity, specificity, PPV, NPV, and diagnostic accuracy of 87.5%, 85.7%, 77.8%, 92.3%, and 86.4%, respectively. However, HCVcAg cutoff point of 3.42 Peiu/ml exhibited sensitivity, specificity, PPV, NPV, and diagnostic accuracy of 100%, 87.5%, 85.7%, 100%, and 92.9% respectively for differentiation between moderate and sever viremia. In another study by Sayed et al., the Roc curve showed that the best cutoff point between mild viremia patients and moderate viremia was found > 2.3 with a sensitivity of 81.25%, specificity of 100.0%, PPV of 100.0%, and NPV of 88.9%. While Roc curve for HCVcAg between moderate and severe viremia showed that the best cutoff point was > 4.2 with sensitivity of 87.5%, specificity of 93.75%, PPV of 87.5%, and NPV of 93.7% [25].
The introduction of DAAs therapies has revolutionized the treatment response of HCV. In this context, we explored the relevance of HCVcAg testing to evaluate the potential role in monitoring virologic response to the new regimen of protease inhibitor-based therapy. In the current work, 92.9% (260/280) of the studied cases achieved sustained virologic response, 3.6% (10/280) were non-responders with persistent viremia throughout the course of the study, and 3.6% (10/280) had recurrent viremia/relapse after completing treatment as proved by RT-PCR results. These results were almost comparable to the rates reported by Nouh et al. (95.8% of patients achieved SVR-12 and 4.2% were non-responders) [26]. Rockstroh et al. also postulated that advances in the treatment of HCV infection with DAAs have demonstrated over 90% cure rates, as defined by the SVR-12. With these therapies, high SVR rates can be obtained regardless of viral genotype, degree of liver fibrosis, or previous treatment history in the majority of patient groups [27].
Regarding relapse, in this study 3.6% of the enrolled patients had a relapse/recurrent viremia as proved by RT-PCR results after 3 months from completing treatment with the DAA combination therapy. Other studies conducted by Wang et al. and Rutter et al. revealed that about 13% of cases had relapse 3 months after completing treatment regimen with DAAs. They suggested that relapsed cases are probably attributed to emergence of treatment resistance-associated variants with reduced replication fitness compared with the wild type virus. If these resistance-associated variants cannot be eliminated by the required combination regimen, strains with reduced replication fitness may persist in low concentration and may account for late relapses [16, 28].
Interestingly, HCVcAg was able to detect 100% (260/260) of patients who achieved SVR-12, 100% (10/10) of those who were non-responders, and 100% (10/10) of patients who developed recurrent viremia/relapse during post-treatment follow-up (sensitivity, specificity, PPV, NPV, and diagnostic accuracy of 100% in relation to PCR results). In the same field, Pischke et al. studied a group of patients who had received DAAs and concluded that early response to treatment could be assessed by the less-expensive HCVcAg assay with equal reliability as PCR testing; therefore, both assays allowed prediction of SVR-12 with the same accuracy [29]. Aghemo et al. also reported that concordance between the two tests in identifying patients who achieved SVR-12 was almost perfect where HCVcAg identified 97% of these patients [30]. In their study about the clinical utility of HCVcAg assay in the monitoring of DAAs for chronic hepatitis C, Lin et al. declared that the HCVcAg assay identified 99% of patients with SVR-12 and that both undetectability of serum HCVcAg and HCV RNA had a high positive predictive value at week 2 (98% vs. 100%) and at week 4 (97% vs. 99%) in predicting SVR-12 [8].
Regarding sensitivity and specificity of HCVcAg for assessment of post-treatment viremia, many studies were nearly parallel to our result; Arboledas et al. [31] reported that the sensitivity of HCVcAg test was 86.5% and Daniel et al. [32] showed 85.3% sensitivity. Meanwhile, Ergunay et al. [33] revealed 75.8% sensitivity. A group of studies recorded sensitivity of more than 90%, ranging from 93.26 to 96.3% as documented by Kotb et al. and Demircili et al. [34, 35]. Miedouge et al. reported that HCVcAg sensitivity was 100% [36].
In their studies, Kesli et al. and Demircili et al. [4, 35] showed results which were almost comparable to current results as regards specificity (100%). Ergunay et al. [33] revealed 95.1% specificity, while Miedouge et al. and Medici et al. respectively found 99.2% and 97.9% specificity for HCVcAg quantitative assays versus nucleic acid-based test [36, 37].
In the year 2018, the European Association for the Study of the Liver recommended that HCVcAg in serum or plasma is a marker of HCV replication that can be used instead of HCV RNA to diagnose acute or chronic HCV infection when HCV RNA assays are not available and/or not affordable. HCVcAg is an easy test with comparable sensitivity (> 90%) and satisfactory correlation with the HCV RNA. Quantification of HCVcAg is to be suggested as an attractive alternative to these expensive and demanding measurements [14].