Impact of SARS-CoV-2 Infection on Erythropoietin Resistance Index in Hemodialysis Patients

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

-  The aim of the study was to show that patients with SARS-CoV-2 infection were resistant to the use of ESAs and required higher doses in the acute phase, possibly due to inflammation, as well as male gender.

 

- The limitations are the small sample size of 25 HD patients and up to 15 with a history of SARS-CoV-2 infection.

- The introduction is significantly long and has parts that are not related to the research!

- The methodology lacks Ethical approval from the institution where the retrospective study was conducted.

- Figure 1 should not be included in the statistical analysis, but should be moved to the results!

- Which stimulants were given to patients with cancer, given that most ESAs are contraindicated?

- Is it necessary to add residual renal function, Kt-V and length of dialysis stay to Table 2?

- Is the underlying disease also necessary, since it is known that some groups of patients have greater resistance?

- Shorten the story for CKD, since this concerns all patients with EDKD and treated with HD?

Author Response

Comment 1:  The aim of the study was to show that patients with SARS-CoV-2 infection were resistant to the use of ESAs and required higher doses in the acute phase, possibly due to inflammation, as well as male gender. The limitations are the small sample size of 25 HD patients and up to 15 with a history of SARS-CoV-2 infection.

Answer 1: We acknowledge that the small sample size (25 HD patients, including 15 with a history of SARS-CoV-2 infection) is a limitation of our study. However, despite this limitation, our research addresses a previously underexplored question, contributing to valuable preliminary insights. Moreover, these results will help guide future research efforts and contribute to a growing body of evidence in this area.

Comment 2: The introduction is significantly long and has parts that are not related to the research!

Answer 2: We thank you for your constructive suggestions, which help us to optimize the content of our research. We extensively revised the Introduction section to make it more concise and fitting with the research project. We felt it was important to fully explain the scientific literature on this topic and illustrate all possible links between haemodialysis status and the impact of covid on anemia parameters (see removed lines in the revised version in the introduction).

Comment 3: The methodology lacks Ethical approval from the institution where the retrospective study was conducted.

Answer 3: We improved information about Ethical approvation in the Methods section (see lines 115-117): “The research protocol was approved by the Local Ethics Committee for Medical Research of Messina (C.E. prot. n. 03-22, approved on 15^th March 2022) and carried out in accordance with the 1964 Declaration of Helsinki and its later amendments”.

Comment 4: Figure 1 should not be included in the statistical analysis, but should be moved to the results!

Answer 4: We moved the Figure 1 to the results before discussion of regression models (see lines 199-207).

Comment 5: Which stimulants were given to patients with cancer, given that most ESAs are contraindicated?

Answer 5: Thank you for your question. Our patients had non-hematologic malignancies, and erythropoiesis-stimulating agents (ESAs) are approved for the treatment of symptomatic anemia in cancer patients. In our study, we primarily used epoetin alfa and darbepoetin, following the recommendations outlined in the KDIGO guidelines on anemia management. While ESAs are associated with an increased risk of thrombotic vascular events, they do not appear to increase overall mortality and, in some cases, may even reduce mortality risk while significantly decreasing the need for blood transfusions. These effects have been observed in studies evaluating ESA use in cancer patients (Tong et al., 2024, doi: 10.1007/s10238-024-01391-3; Heregger & Greil, 2023, doi: 10.1007/s12254-023-00902-4).

Comment 6: Is it necessary to add residual renal function, Kt-V and length of dialysis stay to Table 2?

Answer 6: 

Thank you for your insightful comment. In response to your suggestion, we have added Kt/V and dialysis duration to Tables 1 and 2, as well as to the regression models. However, residual renal function (RRF) was not included because most of our patients either had no measurable RRF or were unable to collect residual urine for an accurate calculation. The available literature suggests that RRF may not be able to influence ERI and need for erythropoiesis-stimulating agents (ESAs) (Louw & Chothia, 2017, doi: 10.1186/s12882-017-0752-x). However, given the limitations in our dataset, we were unable to assess this relationship in our study. We recognize the potential significance of RRF in anemia management, and this remains an important area for future larger-scale studies. To address this limitation, we have explicitly acknowledged the lack of RRF data in the study’s limitations section (see lines 326-330: “Finally, our study lacked information about individual’s residual renal function (RRF) data, as most patients either had no measurable RRF or were unable to provide residual urine for accurate assessment. Despite previous studies have shown no association between RRF and ERI[42], future studies with a larger cohort and comprehensive RRF data collection will be essential to further clarify this relationship”.).

Comment 7: Is the underlying disease also necessary, since it is known that some groups of patients have greater resistance?
Answer 7: Thank you so much for this comment. We completely agree with you and have now added the information on the underlying diseases and causes of ESRD, which can help to better understand the overall picture and create a profile of the patient (See table 1); however, as hypertension and diabetes were already present in table 2 and 3 (and they are also the commonest causes of ESRD), we did not add causes of ESRD to regression models.

Comment 8: Shorten the story for CKD, since this concerns all patients with EDKD and treated with HD?

Answer 8: We agree with you. The CKD section was quite detailed and at risk of diverging from the main focus. We have streamlined it to ensure clarity and alignment with the core theme (see removed lines in the introduction).

 

Reviewer 2 Report

Comments and Suggestions for Authors

This interesting and well-written study describes for the first time the negative impact of SARS-COV2 infection in dialysis patients on anaemia treatment and the induction by COVID 19 infection of a transient hypo-response period to ESA with a significant increase in the erythropoietin resistance index (ERI). This retrospective study used statistical methods that appear robust.

Author Response

Comment 1: This interesting and well-written study describes for the first time the negative impact of SARS-COV2 infection in dialysis patients on anaemia treatment and the induction by COVID 19 infection of a transient hypo-response period to ESA with a significant increase in the erythropoietin resistance index (ERI). This retrospective study used statistical methods that appear robust.

Answer 1: We sincerely appreciate your positive feedback and thoughtful evaluation of our study. We are pleased that you found our research well-written and valuable in highlighting the impact of SARS-CoV-2 infection on anemia treatment in dialysis patients. We believe that our study provides a oundation for future research on the interplay between COVID-19, anemia management, and ESA responsiveness in dialysis patients. Thank you for your valuable review and support of our work.

Reviewer 3 Report

Comments and Suggestions for Authors

Thank you for the opportunity to review the article, as it is of significant interest to specialists, originality and relevance. The problem of anemia in patients with progressive renal failure is one of the determining factors for the quality and duration of life in such patients. It is interesting to determine the contribution of coronavirus infection to the development of resistance to erythropoietin. I have several comments: 1) regarding the study design, it is difficult to call it a cohort study, since a cohort study is observational and assumes the absence of any interventions. In addition, a very small sample (only 25 patients, including the main and control groups) also does not allow this study to be classified as a cohort study; 2) Abbreviations should be described in the text, in Table 1 the TSAT abbreviation has no decoding; 3) did the authors study such indicators of iron deficiency anemia as serum iron, TIBC, percentage of transferrin saturation?

Author Response

Comment 1: Thank you for the opportunity to review the article, as it is of significant interest to specialists, originality and relevance. The problem of anemia in patients with progressive renal failure is one of the determining factors for the quality and duration of life in such patients. It is interesting to determine the contribution of coronavirus infection to the development of resistance to erythropoietin. I have several comments: 1) regarding the study design, it is difficult to call it a cohort study, since a cohort study is observational and assumes the absence of any interventions. In addition, a very small sample (only 25 patients, including the main and control groups) also does not allow this study to be classified as a cohort study.

Answer 1: Thank you for appreciating our work and giving us insightful feedbacks. We acknowledge that the study design does not fully align with the traditional definition of a cohort study, as it involved a limited sample size. We reconsidered the terminology used to describe the study and ensure that it is classified appropriately to reflect its design more accurately and simply define it as a “small-scale retrospective study”.

Comment 2: Abbreviations should be described in the text, in Table 1 the TSAT abbreviation has no decoding.

Answer 2: We have added a list of abbreviations at the end of the paper to make it easier to read and written out the acronyms at their first appearance in the text (See table 1 notes and the list of abbreviations at the end of the paper).

Comment 3: Did the authors study such indicators of iron deficiency anemia as serum iron, TIBC, percentage of transferrin saturation? 

Answer 3: We have added indicators of iron deficiency anemia to table 1 and 2; however, they had a negligible impact on ERI trend between T1 and T2, and presence of missing data on laboratory values at the follow-up visits did not allow to explore their impact on subsequent ERI changes between T2 and T4.

 

 

Reviewer 4 Report

Comments and Suggestions for Authors

The work presented a relevant theme for science, with great clinical applicability. I leave only some questions and suggestions for a better understanding of the data.

Pag. 3 - The statistics have already been run, at this point it should be specified which variables presented a normal distribution.

Pag. 4 - The statistics have already been run, at this point it should be specified which variables presented a normal distribution.

Pag. 4 - Table 1 - The table requires review of the parameters presented, in addition to standardizing the format in which the data is presented.

Pag. 5 - I suggest grouping by group and not by time.

Author Response

Comment 1: The work presented a relevant theme for science, with great clinical applicability. I leave only some questions and suggestions for a better understanding of the data. Pag. 3 - The statistics have already been run, at this point it should be specified which variables presented a normal distribution.

Answer 1: Thank you so much for this suggestion. We added a brief description of normal and not normally distributed continuous variables at lines 131-133: “Continuous variables with a normal distribution were represented by age and length of dialysis; conversely, laboratory values and ERI were not normally distributed”.

Comment 2: Pag. 4 - The statistics have already been run, at this point it should be specified which variables presented a normal distribution. 

Answer 2: See comment above.

Comment 3:Pag. 4 - Table 1 - The table requires review of the parameters presented, in addition to standardizing the format in which the data is presented.

Answer 3: We reviewed all parameters presented. Continuous variables with a normal distribution were age and length of dialysis, while not normally distributed ones included those summarized with median (IQR), such as laboratory values and ERI.

Comment 4: Pag. 5 - I suggest grouping by group and not by time.

Answer 4: Thank you for your valuable comment. The figure employs a dual stratification approach: first by group (represented by different colors) and then by time (indicated by different x-axis ticks). This design allows for a clear visualization of the ERI trend over time within each group, facilitating the interpretation of dynamic changes. Given that the figure introduces the concept of ERI trend, which serves as the outcome variable in the subsequent regression models, we believe this stratification method effectively supports the study’s objectives. Therefore, we have opted to retain this representation.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

No

Reviewer 3 Report

Comments and Suggestions for Authors

I am satisfied with the changes made by the authors