The role of hepatitis B virus core-related antigen in predicting hepatitis B virus relapse after cessation of entecavir in hepatitis B e antigen-negative patients

EASL Clinical Practice Guidelines on the management of hepatitis B virus infection

The updated EASL Clinical Practice Guidelines on the management of hepatitis B virus (HBV) infection provide comprehensive, evidence-based recommendations for its management. Spanning ten thematic sections, the guidelines address diagnostics, treatment goals, treatment indications, therapeutic options, hepatocellular carcinoma surveillance, management of special populations, HBV reactivation prophylaxis, post-transplant care, HBV prevention strategies, and finally address open questions and future research directions. Chronic HBV remains a global health challenge, with over 250 million individuals affected and significant mortality due to cirrhosis and hepatocellular carcinoma. These guidelines emphasise the importance of early diagnosis, risk stratification based on viral and host factors, and tailored antiviral therapy. Attention is given to simplified algorithms, vaccination, and screening to support global HBV elimination targets. The guidelines also discuss emerging biomarkers and evolving definitions of functional and partial cure. Developed through literature review, expert consensus, and a Delphi process, the guidelines aim to equip healthcare providers across disciplines with practical tools to optimise HBV care and outcomes worldwide.

Hepatitis B Surface Antigen Seroclearance Rate After Stopping Nucleos(t)ide Analogues in Chronic Hepatitis B-A Systematic Review and Meta-Analysis

AIM

To identify factors influencing HBsAg seroclearance rates after stopping nucleos(t)ide analogue (NA) therapy in patients with chronic hepatitis B (CHB).

METHODS

We conducted a comprehensive literature search in databases from inception to July 2024. Subgroup analyses and meta-regression were performed to determine factors associated with HBsAg seroclearance, including ethnicity, HBV genotype, NA therapy duration, end-of-treatment (EOT) qHBsAg levels, HBeAg status, cirrhosis status, and follow-up duration.

RESULTS

The meta-analysis included 62 studies (n = 9867) with a pooled HBsAg seroclearance rate of 10% (95%CI: 8%-12%, I2 = 92%) after NA cessation. HBeAg-negative patients showed significantly higher rates than HBeAg-positive patients (11% vs. 5%, p = 0.030). Subgroup analysis revealed higher seroclearance with follow-up of >5 years (18%, p = 0.004), showing significantly higher rates were observed in studies with longer follow-up periods. Caucasians showed a higher rate (12%) than Asians (9%, p = 0.067). Studies adhering to AASLD, EASL, or APASL stopping rules showed no significant differences in rates. Patients with EOT qHBsAg ≤2.0 log IU/mL had higher rates (23%) than those with >2.0 log IU/mL (11%). Re-treated patients had lower seroclearance (6%) compared to those not re-treated (17%, p = 0.178). Meta-regression identified ethnicity, HBeAg status, and follow-up duration as significant contributors to heterogeneity. Egger's test showed no evidence of publication bias (p = 0.1928).

CONCLUSION

Our meta-analysis highlights the role of ethnicity, EOT qHBsAg levels, HBeAg-status, and follow-up duration in determining HBsAg seroclearance rates. These findings stress the need for personalized NA discontinuation strategies and further research on HBV genotypes and biomarkers to improve treatment outcomes and predict seroclearance more accurately.

Hepatitis B core-related antigen as a promising serological marker for monitoring hepatitis B virus cure

Hepatitis B virus (HBV) infection is a global health concern. The current sequential endpoints for the treatment of HBV infection include viral suppression, hepatitis B e antigen (HBeAg) seroconversion, functional cure, and covalently closed circular DNA (cccDNA) clearance. Serum hepatitis B core-related antigen (HBcrAg) is an emerging HBV marker comprising three components: HBeAg, hepatitis B core antigen, and p22cr. It responds well to the transcriptional activity of cccDNA in the patient's liver and is a promising alternative marker for serological testing. There is a strong correlation, and a decrease in its level corresponds to sustained viral suppression. In patients with chronic hepatitis B (CHB), serum HBcrAg levels are good predictors of HBeAg seroconversion (both spontaneous and after antiviral therapy), particularly in HBeAg-positive patients. Both low baseline HBcrAg levels and decreasing levels early in antiviral therapy favored HBsAg seroconversion, which may serve as a good surrogate option for treatment endpoints. In this review, we summarize the role of serum HBcrAg in the treatment of CHB. Therefore, long-term continuous monitoring of serum HBcrAg levels contributes to the clinical management of patients with CHB and optimizes the choice of treatment regimen, making it a promising marker for monitoring HBV cure.

HBV Biomarkers and Their Role in Guiding Treatment Decisions

Over 300 million individuals worldwide are chronically infected with hepatitis B virus and at risk for progressive liver disease. Due to the lack of a therapy that reliably achieves viral elimination and the variability of liver disease progression, treatment decisions are guided by the degree of liver disease and viral biomarkers as the viral life-cycle is well characterized and largely conserved between individuals. In contrast, the immunological landscape is much more heterogeneous and diverse and the measurement of its components is less well standardized. Due to the lack of a universal and easily measurable set of biomarkers, clinical practice guidelines remain controversial, aiming for a balance between simplifying treatment decisions by reducing biomarker requirements and using all available biomarkers to avoid overtreatment of patients with low risk for disease progression. While approved therapies such as nucleos(t)ide analogs improve patient outcomes, the inability to achieve a complete cure highlights the need for novel therapies. Since no treatment candidate has demonstrated universal efficacy, biomarkers will remain important for treatment stratification. Here, we summarize the current knowledge on virological and immunological biomarkers with a specific focus on how they might be beneficial in guiding treatment decisions in chronic hepatitis B.

Discontinuation of Nucleos(t)ide Analogues in HBeAg Negative Chronic Hepatitis B Patients: Risks and Benefits

Chronic hepatitis B (CHB) remains a major threat to global public health, affecting 296 million people worldwide. Although there is no curative treatment for CHB today, the virus can be effectively controlled with current antiviral treatment strategies. Since HBsAg loss can rarely (1%) be achieved with current nucleos(t)ide analogues (NA) options, lifelong treatment is usually required in HBeAg-negative patients. In recent years, guidelines have stated that long-term NA treatments can be discontinued for HBeAg-negative patients without achieving HBsAg loss. There is no general consensus on how discontinuation of NA can be included in the treatment approach. This review aimed to evaluate the current literature regarding the discontinuation of NA treatment in HBeAg-negative patients. Patients with HBeAg-negative CHB who have a higher chance of response after discontinuation of NA therapy can be defined as non-cirrhotic patients who have low HBsAg, HBcrAg, and HBV RNA levels at the discontinuation of treatment and accept close follow-up. The management of relapses that develop after NA discontinuation in patients is also unclear. The agent used in NA treatment itself may also affect the pattern of relapse development. Relapse after NA treatment occurs significantly slower and less frequently with entecavir compared to other regimens, including tenofovir dipivoxil. Prospective studies are needed in order to maintain the chance of HBsAg clearance in case of exacerbation and to treat acute exacerbations that can be fatal in a timely manner. Algorithms to be developed for use after discontinuation of NA treatment will help the clinician manage the patient safely.

Quantitative Measurement of Serum HBcrAg Can Be Used to Assess the Feasibility of Safe Discontinuation of Antiviral Therapy for Chronic Hepatitis B

Hepatitis B virus (HBV) infection is a serious global health problem, and chronic HBV infection significantly increases the risk of liver fibrosis, cirrhosis, and even hepatocellular carcinoma in patients. Current first-line therapeutics such as nucleos(t)ide analogues and interferons are unable to completely clear cccDNA, so the vast majority of patients need to take long-term or even lifelong medication. However, long-term virological and biochemical responses can be achieved in some patients after drug withdrawal. Successfully screening these patients with drug withdrawal advantages is difficult. Hepatitis-B-core-related antigen (HBcrAg) is a new HBV serological marker that which can reflect the level and transcription activity of cccDNA in hepatocytes. Therefore, HBcrAg has potential value in guiding patients in drug withdrawal. This review summarizes previous reports on HBcrAg and evaluates the application value of HBcrAg in safe drug discontinuation.

Higher end-of-treatment HBsAg levels is associated with later onset but not severe relapse in HBeAg-negative chronic hepatitis B patients stopping antivirals

BACKGROUND

Quantitative hepatitis B surface antigen (qHBsAg) level at end-of-treatment (EOT) predict clinical relapse (CR) after nucleos(t)ide analogues (Nuc) in chronic hepatitis B(CHB) patients. It is unclear if higher EOT qHBsAg leads to earlier onset or more severe off-Nuc CR.

AIM

This large cohort study investigates the association between EOT qHBsAg and CR onset/severity.

METHODS

This study enrolled HBeAg-negative CHB patients who had achieved undetectable HBV DNA for over 1 year after receiving Nuc therapy before discontinuation. The EOT qHBsAg level was categorised into three groups: <100, 100-999, ≥1000 IU/mL. The study assessed the predictability of qHBsAg levels for CR, and analysed and compared the incidence, time to onset and severity of CR among these three groups.

RESULTS

Patients with higher EOT qHBsAg showed a higher incidence of CR (≥1000, 100-999, <100 IU/mL: 73%, 65%, and 38%, p < 0.01) but a later onset of CR (median time to CR: 35, 33 and 27 weeks, p < 0.01). The predictabilities of EOT qHBsAg for CR were greater in patients aged <50-year-old or with genotype C than in those aged ≥50-year-old or with genotype B. There's no correlation between EOT qHBsAg level and ALT folds at CR (Pearson correlation coefficient: r = -0.03, p = 0.35). EOT qHBsAg was neither a predictor for severe hepatitis flare nor a predictor for hepatic decompensation.

CONCLUSIONS

Predictability using EOT qHBsAg levels for CR differed in subgroups of age and genotypes. Higher EOT qHBsAg levels correlate with higher incidence but later onset of CR. No correlation between EOT qHBsAg and relapse severity was observed.

Hepatitis Flares or Hepatic Decompensation after Discontinuation of Tenofovir Disoproxil Fumarate and Entecavir in Non-Cirrhotic Hepatitis B e Antigen-Negative Patients

Hepatic events can occur after discontinuing antiviral therapy. We investigated factors associated with hepatitis flares and hepatic decompensation after discontinuing tenofovir disoproxil fumarate (TDF) and entecavir (ETV). Hepatitis flares within 6 months and hepatic decompensation were compared between non-cirrhotic hepatitis B e antigen-negative patients after discontinuing TDF or ETV by using the Cox proportional hazard model. The cumulative rates of hepatitis flare at 6 months after discontinuing ETV and TDF were 2% and 19%, respectively (p < 0.001). The respective rates of hepatic decompensation at 6 months were 0% and 7% (p = 0.009). Higher alanine aminotransferase (ALT) (AASLD criteria) at the end of treatment (EOT) (HR = 4.93; p = 0.001), an off-therapy dynamic change in HBV DNA (rapid rebound of HBV DNA from the nadir, ≥1 log10 IU/mL per month) (HR = 10.7; p < 0.001), and the discontinuation of TDF (HR = 6.44; p = 0.006) were independently associated with hepatitis flares within 6 months. Older age (HR = 1.06; p < 0.001) and an off-therapy dynamic change in HBV DNA (HR = 3.26; p = 0.028) were independently associated with hepatic decompensation after the discontinuation of antiviral therapy. In summary, we demonstrated several factors associated with hepatitis flares and hepatic decompensation after discontinuing antiviral therapy in non-cirrhotic hepatitis B e antigen-negative patients.

Hepatitis B core-related antigen: A novel and promising surrogate biomarker to guide anti-hepatitis B virus therapy

The current requirement for biomarkers to detect hepatitis B virus (HBV) infection is polarized. One is a fully-automated and highly sensitive measurement system; the other is a simple system for point-of-care testing (POCT) in resource-limited areas. Hepatitis B core-related antigen (HBcrAg) reflects intrahepatic covalently closed circular DNA and serum HBV DNA. Even in patients with undetectable serum HBV DNA or HBsAg loss, HBcrAg may remain detectable. Decreased HBcrAg levels are associated with reduction of the occurrence of hepatocellular carcinoma (HCC) in chronic hepatitis B. Recently, a fully-automated, novel high-sensitivity HBcrAg assay (iTACT-HBcrAg, cut-off value: 2.1 logIU/mL) has been developed. This attractive assay has been released in Japan very recently. iTACT-HBcrAg can be useful for monitoring HBV reactivation and prediction of HCC occurrence, as an alternative to HBV DNA. Moreover, monitoring HBcrAg may be suitable for determining the therapeutic effectiveness of approved drugs and novel drugs under development. Presently, international guidelines recommend anti-HBV prophylaxis for pregnant women with high viral loads to prevent mother-to-child transmission of HBV. However, >95% of HBV-infected individuals live in countries where HBV DNA quantification is not available. Worldwide elimination of HBV needs the scaling-up of examination and medication services in resource-limited areas. Based on this situation, a rapid and easy HBcrAg assay as a POCT is valuable. This review provides the latest information regarding the clinical use of a new surrogate marker, HBcrAg, in HBV management, based on iTACT-HBcrAg or POCT, and introduces novel agents targeting HBV RNA/protein.

Safety considerations for withdrawal of nucleos(t)ide analogues in patients with chronic hepatitis B: First, do no harm

Nucleos(t)ide analogues (NA) are widely used to treat hepatitis B virus (HBV) infection, but they cannot eradicate the virus and treatment duration can be lifelong if the endpoint is set at seroclearance of the hepatitis B surface antigen (HBsAg). As an alternative strategy, finite NA therapy without the prerequisite of HBsAg seroclearance has been proposed to allow treatment cessation in patients with sustained undetectable HBV viremia for two to three years. However, reactivation of viral replication almost always follows NA withdrawal. Whereas HBV reactivation might facilitate HBsAg seroclearance in some, it could lead to serious acute flare-ups in a certain proportion of patients. Occurrence and consequences of NA withdrawal flares are complicated with various factors involving the virus, host, and treatment. Accurate risk prediction for severe flares following NA cessation is essential to ensure patient safety. The risks of life-threatening flares in patients who discontinued NA according to the stopping rules of current guidelines or local reimbursement policies have recently been quantitatively estimated in large-scale studies, which also provided empirical evidence to help identify vulnerable patients at risk of devastating outcomes. Moreover, risk predictors were further explored and validated to hopefully aid in patient selection and management. In this narrative review with a focus on patient safety, we summarize and discuss current literature on the incidence of severe flares following NA cessation, risk stratification for candidate selection, rules of posttreatment monitoring, and indications for treatment resumption. We also share our thoughts on the limitations of existing knowledge and suggestions for future research.

Utility of novel viral and immune markers in predicting HBV treatment endpoints: A systematic review of treatment discontinuation studies

Background & Aims

Antivirals represent the mainstay of chronic hepatitis B treatment given their efficacy and tolerability, but rates of functional cure remain low during long-term therapy. Treatment discontinuation has emerged as a strategy to maintain partial cure and achieve functional cure in select patient groups. We aimed to evaluate how data from treatment discontinuation studies exploring novel viral and/or immune markers could be applied to the functional cure program.

Methods

Treatment discontinuation studies evaluating novel viral and/or immune markers were identified by a systematic search of the PubMed database through to October 30, 2022. Data extraction focused on information regarding novel markers, including identified cut-off levels, timing of measurement, and associated effect on study outcomes of virological relapse, clinical relapse, and HBsAg seroclearance.

Results

From a search of 4,492 citations, 33 studies comprising a minimum of 2,986 unique patients met the inclusion criteria. Novel viral markers, HBcrAg and HBV RNA, were demonstrated across most studies to be helpful in predicting off-therapy partial cure, with emerging evidence to support a link with functional cure. From novel immune marker studies, we observed that treatment discontinuation has the potential to trigger immune restoration, which may be associated with a transient virological relapse. To this end, these studies support the combination of virus-directing agents with immunomodulator therapies to induce two key steps underlying functional cure: viral antigen load reduction and restoration of the host immune response.

Conclusions

Patients with a favourable profile of novel viral and immune markers stand to benefit from a trial of antiviral treatment discontinuation alongside novel virus-directing agents with the aim of achieving functional cure without excessive risk of severe clinical relapse.

Impact and implications

Select patients with chronic hepatitis B undergoing nucleoside analogue therapy may benefit from a trial of treatment discontinuation, aiming to maintain partial cure and/or achieve functional cure. We propose a profile of novel viral and immune markers to identify patients who are likely to achieve these goals without excessive risk of hepatic decompensation. Furthermore, treatment discontinuation may also be considered as a therapeutic strategy to trigger immune restoration, which may increase the chance of functional cure when used in conjunction with novel virus-directing agents.

A critique and systematic review of the clinical utility of hepatitis B core-related antigen

BACKGROUND & AIMS

Hepatitis B core-related antigen (HBcrAg) is a new biomarker for chronic hepatitis B (CHB) whose performance has not been critically or systematically appraised. Herein, we performed a systematic review to determine its clinical utility.

METHODS

We evaluated the biological pathway of HBcrAg and performed a systematic review of PubMed for clinical trials, cohort studies, and case-control studies that evaluated the clinical utility of HBcrAg. The effectiveness of HBcrAg in predicting HBV-specific clinical events (e.g. HBeAg seroconversion, phases of CHB, HBsAg loss, treatment response, and relapse after stopping therapy) was examined using receiver-operating characteristic curves. The correlation coefficients of HBcrAg with HBV DNA, quantitative HBsAg (qHBsAg), HBV RNA, and cccDNA were summarised from published studies. Median values were used as estimates.

RESULTS

HBcrAg consists of three precore/core protein products: HBcAg, HBeAg, and a 22 kDa precore protein. HBcrAg assays have been associated with false-positive rates of 9.3% and false-negative rates of between 12-35% for CHB. The new iTACT-HBcrAg is more sensitive but does not reduce the false-positive rate. A PubMed search found 248 papers on HBcrAg, of which 59 were suitable for analysis. The clinical performance of HBcrAg was evaluated using AUROC analyses, with median AUROCs of 0.860 for HBeAg seroconversion, 0.867 for predicting HBeAg(-) hepatitis, 0.645 for HBsAg loss, 0.757 for treatment response, and 0.688 for relapse after stopping therapy. The median correlation coefficient (r) was 0.630 with HBV DNA, 0.414 with qHBsAg, 0.619 with HBV RNA and 0.550 with cccDNA. Correlation decreased during antiviral therapy, but combined biomarkers improved performance.

CONCLUSIONS

HBcrAg has a mixed performance and has a poor correlation with HBsAg loss and antiviral therapy, hence HBcrAg results should be interpreted with caution.

IMPACT AND IMPLICATIONS

Hepatitis B core-related antigen (HBcrAg) has been used to assess management of patients with chronic hepatitis B (CHB) without a systematic and critical Sreview of its performance. Our finding that HBcrAg had a false-positive rate of 9% and a false-negative rate of 12-35% raises concerns, although larger studies are needed for validation. A systematic review showed that the performance of HBcrAg was variable depending on the CHB endpoint; it was excellent at predicting HBeAg seroconversion and HBeAg-negative chronic hepatitis (vs. chronic infection), which should be its main use, but it was poor for relapse after stopping antiviral therapy and for HBsAg loss. HBcrAg results should be interpreted with considerable caution, particularly by physicians, researchers, guideline committees and agencies that approve diagnostic tests.

Tenofovir versus entecavir for tertiary prevention of hepatocellular carcinoma in chronic hepatitis B infection after curative therapy: A systematic review and meta-analysis

Entecavir (ETV) and Tenofovir disoproxil fumarate (TDF) are the first-line drugs for the treatment of chronic hepatitis B virus (HBV). However, the impact of these two antiviral agents on the outcome of HBV-related hepatocellular carcinoma (HCC) after curative therapy remains to be explored. The purpose of the present study was to compare the effect of ETV and TDF on recurrence and mortality after curative treatment for HBV-related HCC. A comprehensive literature search of multiple electronic databases was conducted from 2000 to January 2022 for studies comparing ETV and TDF for HBV-related HCC patients after curative therapy. The adjusted hazard ratios (aHR) were pooled using a random-effects model. A total of nine studies with 5298 patients were included in the final meta-analysis. TDF was associated with a lower risk of HCC recurrence [aHR 0.73, 95% confidence interval (CI) 0.65-0.81] compared to HCC. TDF reduced the risk of late recurrence compared to ETV (aHR 0.58, 95% CI 0.45-0.76) but not early recurrence (aHR 0.88, 95% CI 0.76-1.02). The mortality risk was also lower with TDF compared to ETV (aHR 0.62, 95% CI 0.50-0.77). TDF was associated with a lower risk of recurrence and mortality than ETV after resection or ablation of HBV-related HCC. Further prospective randomized controlled studies are warranted to validate these results.

Serum Pregenomic RNA Combined With Hepatitis B Core-Related Antigen Helps Predict the Risk of Virological Relapse After Discontinuation of Nucleos(t)ide Analogs in Patients With Chronic Hepatitis B

BACKGROUND AND AIM

Cessation of nucleos(t)ide analogs (NAs) therapy in patients with chronic hepatitis B (CHB) is uncommon. Although criteria for discontinuation appear in some guidelines, the indicators for assessing discontinuation of NAs are limited, whether NAs can be safely ceased remains a difficult clinical issue. Our study aimed to investigate the role of serum pregenomic RNA (pgRNA) and hepatitis B core-related antigen (HBcrAg) at the end of treatment (EOT) in guiding the safe discontinuation of NAs in CHB patients.

METHODS

This is a retrospective study, clinical data of all CHB patients who discontinued NAs treatment at West China Hospital between June 2020 and January 2021 were collected, including EOT pgRNA, HBcrAg, hepatitis B surface antigen (HBsAg), etc. All patients should meet the Asian-Pacific guideline for discontinuation. Observing virological relapse (VR) rates during 1 year of NAs discontinuation and analyzing the relationship between EOT pgRNA, HBcrAg, and VR.

RESULTS

A total of 64 patients were enrolled in this study and 33 (51.5%) patients experienced VR in 1 year. EOT pgRNA positivity (OR = 14.59, p = 0.026) and EOT higher HBcrAg levels (OR = 14.14, p = 0.001) were independent risk factors for VR. The area under the receiver-operating characteristic (AUROC) value of EOT HBcrAg for VR was 0.817 (p < 0.001), optimal cut-off value was 3.3 log10 U/mL. Patients with EOT pgRNA positivity and EOT HBcrAg >3.3 log10 U/mL were more likely to experience VR after discontinuation of NAs (88.9 vs. 45.5%, p = 0.027).

CONCLUSION

According to current guidelines, a higher VR rate occurs after cessation of NAs. EOT pgRNA positivity and higher HBcrAg level carries a higher risk of VR. Combining these novel markers can better help us assess whether patients can safely cease NAs treatment.

Hepatitis B Core-Related Antigen is a Biomarker for off-Treatment Relapse After Long-Term Nucleos(t)ide Analog Therapy in Patients with Chronic Hepatitis B

Objective

It remains unknown how to stratify the risk of clinical relapse of chronic hepatitis B (CHB) patients after stopping nucleos(t)ide analogs (NAs) antiviral therapy.

Methods

The current post hoc analysis included 122 non-cirrhotic patients with chronic hepatitis B virus infection who were positive for hepatitis B envelope antigen (HBeAg) and discontinued long-term NA therapy after achieving HBeAg seroconversion for a median of 2.5 years. Post hoc analysis of end-of-treatment (EOT) hepatitis B core-related antigen (HBcrAg) levels was performed using a chemiluminescent enzyme immunoassay.

Results

A total of 78/122 (63.9%) patients experienced sustained response after NAs cessation, and 44/122 (36.1%) patients experienced clinical relapse. In multivariate analysis, EOT HBcrAg (hazard ratio [HR] = 2.105 95% CI: 1.440–3.077, p < 0.001), hepatitis B surface antigen (HBsAg) ≥100 IU/mL (HR = 4.406, 95% CI 1.567–12.389, p = 0.005) and age (HR = 1.051, 95% CI: 1.010–1.093, p = 0.049) were independently associated with clinical relapse. A cut-off value of 4.0 log₁₀ U/mL of HBcrAg was defined by maximized Youden’s index. An EOT HBcrAg level of ≥4.0 log₁₀ U/mL was associated with higher risks of clinical relapse (65.8% vs 23.2%, p<0.001) and HBeAg reversion (27.5% vs 1.6%, p < 0.001). In majority of patients (n = 91) who had a high EOT HBsAg level (≥100 IU/mL), serum HBcrAg level could further discriminate patients at low risk of clinical relapse. Patients with an HBcrAg level ≥4.0 log₁₀ U/mL had significantly higher cumulative incidence rates of clinical relapse (78.1% vs 29.4%, p < 0.001) and HBeAg reversion (29.4% vs 0%, p < 0.001).

Conclusion

Serum EOT HBcrAg level can be a predictor of off-treatment relapse in patients with CHB. An HBcrAg level of 4.0 log₁₀ U/mL may identify patients at high risk of clinical relapse after treatment cessation.