Comment on ‘Comparing specificity and seroconversion sensitivity among major blood screening assays for human immunodeficiency virus and viral hepatitis’

We read with considerable interest the recent article by Chaves et al. 1, which addresses important aspects of donor screening for human immunodeficiency virus, hepatitis B virus, and hepatitis C virus (HCV). Comparative evaluations of screening assays are essential for strengthening global blood safety. However, after reviewing the article in detail, we are concerned that the presented design and interpretation of the HCV analyses do not support conclusions of assay ‘superiority’. In particular, the comparison between an antigen/antibody (Ag/Ab) combination assay and antibody-only (Ab-only) assays introduces a biological asymmetry that predetermines the outcome and complicates interpretation. A scientifically balanced evaluation would use comparators with intended use that is identical to the evaluation assay, along with standardized seroconversion panels. The Alinity s Anti-HCV assay is labelled explicitly as an antibody screening test for donor testing, whereas Elecsys HCV Duo measures both Ag and Ab. This comparison does not allow for a robust assessment of analytical sensitivity. More critically, the HCV comparison conflates biomarker biology with assay performance on a specific assay platform. It is well known that HCV core Ag emerges earlier than antibodies during acute infection, shortening the window period relative to Ab-only tests. Chaves et al. 1 report that Elecsys HCV Duo detected infection approximately 1.5 days after nucleic acid amplification technic positivity, compared with roughly 21–24 days for the Ab-only assays. When window period performance is evaluated, marker kinetics—rather than assay engineering—drive early signal appearance, and any conclusions should be drawn in the context of these well-known marker kinetics. Moreover, because no biologically equivalent Ag-plus-antibody comparator exists, previous evaluations have either benchmarked the Ag component against dedicated HCV core Ag assays or reported the diagnostic accuracy of the antibody module of the dual assay separately. This approach avoids conflating different biomarker classes and ensures that comparisons are aligned with the closest available analytical target, as demonstrated in multi-centre and clinical evaluations 2-4. A central question raised by the authors' description is whether their study constitutes a true head-to-head (H2H) comparison. Prior publications provide clear guidance on these methodological expectations 5, 6. Established criteria for H2H evaluations require that assays be run in parallel, ideally within a 2-h interval, to minimize pre-analytical variability. Additional requirements include replicate measurements, consistent environmental conditions and standardized sample handling procedures 7. In contrast, the study by Chaves et al. 1 involved different testing sites, transport of samples for seroconversion evaluation and varying intervals between measurements. Although the limitations section of the article briefly notes sampling interval concerns, this statement addresses precision within seroconversion panels only and does not fully acknowledge the implications for overall study design. In addition to the study design and the resulting selection bias introduced by the seroconversion panel subsets used in the primary evaluation, several other aspects of the study are described ambiguously. The reporting of seroconversion sensitivity using percentage shifts (‘the same, ahead, or behind’) lacks clarity and does not follow standard seroconversion panel terminology. The authors also claim that the HCV Duo assay detects infection across genotypes due to its monoclonal antibody design; however, this conclusion is not supported by the presented data. The study's seroconversion panels originate exclusively from a US donor population, and the resulting analysis includes only the most prevalent genotypes, making the genotype-independence claim unsubstantiated. Furthermore, sensitivity comparisons rely on a small number of archived positive samples that the authors themselves describe as difficult to characterize, which inherently limits the strength and reliability of the conclusions drawn 1. In this context, we welcome continued scientific investigation and open, evidence-based dialogue within the transfusion medicine community. Ongoing research, transparent data sharing and constructive discussion are essential to ensuring the highest standards of blood safety and to advancing the accuracy and reliability of serological testing. We encourage colleagues to contribute further studies and perspectives that help strengthen our collective understanding and support optimal decision-making for donors, patients and laboratories worldwide. We anticipate that the clarifications provided will enable more accurate interpretation and further strengthen the scientific progress underlying donor-screening practices. The authors declare no conflicts of interest. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.