Free Thyroxine as a Predictor of Mortality in Critically Ill Septic Patients—A Retrospective Study

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

REVIEW: DIAGNOSTICS
ARTICLE: Free thyroxine as a predictor of mortality in critically ill septic patients - a seven-year retrospective study
I appreciate the invitation to review this article and congratulate the authors for seeking to clarify the role of T4 in the mortality of septic patients. Below, I present my respectful considerations.

TITLE: partially adequate; it directly translates the results of the study, however, I suggest that the phrase "seven years" be suppressed, since this information is included in the method and removing it makes the title more attractive and does not compromise the content;

ABSTRACT:
Background/Objectives: adequate; they establish that the role of ESS and low T3 is already well defined in septic patients, but the role of T4L is not yet well established;

Methods: partially adequate; I suggest including the reference guide for conducting and writing observational studies (e.g., STROBE) and the level of statistical significance adopted;
Results: partially adequate; I suggest including the confidence interval for AUROC and the p-value of T4 in the multivariate model; differentiate the values ​​for the primary and secondary outcomes;

Conclusions: adequate;

Keywords: adequate;

INTRODUCTION: adequate to the results, conclusion, and title; with fluent language contextualized to the classic and recent literature on the subject; I only suggest that the authors evaluate maintaining the detailed description present in the fifth and sixth paragraphs. I believe that an objective synthesis could be made, without prejudice to the content and making the introduction more direct.

MATERIALS AND METHODS: partially adequate; include the STROBE; describe how APACHE and SOFA were obtained, whether directly from the patient's medical record/data or measured by the researchers and, if it was the first option, cite this as a probable limitation/measurement bias, due to the evaluation having been done by multiple professionals; describe the origin of the laboratory data: whether from hospital routine or specifically collected for the study; to describe the laboratory analysis techniques for these parameters in order to determine a reference/comparison standard for other studies; as well as how quality control was ensured, from sample collection to processing; to describe all the characterization and clinical variables that were investigated and how the data collection, cleaning, consistency, and validation process was carried out.
RESULTS: Analysis of Comorbidities and Clinical Outcome Scores; the authors presented an analysis of comorbidities and their associations with outcomes, which is interesting, however, this is not clearly described in the method and is also not contextualized in the introduction. I do not consider this a problem, but I suggest that in addition to what was done, the authors make a comparison between the TSH and T4 values ​​between survivors and non-survivors in each of the outcome scenarios, according to each comorbidity, so that we can see the relationship between them; The authors state that “APACHE II and SOFA scores, length of stay, and mortality were then compared between these three groups, and no significant difference was found between any of the parameters investigated (Table 4),” however, they present a p-value of 0.044 for 28-day mortality and 0.004 for hospital mortality: clarification is needed; The authors state that “The SOFA score had the best predictive ability, followed by the APACHE II score, for both primary and secondary outcomes,” however, according to Table 6, APACHE showed better prediction for 28-day mortality and SOFA for overall mortality: clarification is needed; what justified the authors using only age, hemoglobin, levels, fT4, and SOFA score for the multivariate analysis, given that the other parameters, except creatinine, were significant for the outcomes? Clarification is needed. I suggest that a new analysis be done with the others. Including Youden's indices and Positive and Negative Predictive Values ​​would add robustness to the results.
DISCUSSION: although the main focus of the discussion is the values ​​of thyroid hormones and mortality, I suggest that the authors dedicate one or two paragraphs to discussing the profile of their patients and whether these are similar to other profiles from Europe, Asia, Africa, and the Americas; I also suggest discussing the findings of comorbidities and how these influence or may be influenced by TSH and T4 dysfunctions.

CONCLUSION: adequate;

REFERENCES: adequate in quantity and quality; up-to-date: >75% published after 2020; studies showed a direct connection with the content of the article under evaluation.

Author Response

Thank you very much for your comments on our manuscript. Please find below a point-by-point response to the requested changes:

Comment 1: TITLE: partially adequate; it directly translates the results of the study, however, I suggest that the phrase "seven years" be suppressed, since this information is included in the method and removing it makes the title more attractive and does not compromise the content.

Response 1: The phrase "seven years" has been removed.

 

Comment 2: Methods: partially adequate; I suggest including the reference guide for conducting and writing observational studies (e.g., STROBE) and the level of statistical significance adopted.

Response 2: We have added the "STROBE-compliant" flowchart in Figure 1 and added the following clarification in the Materials and Methods section: "We included, in this STROBE compliant, observational study, patients with sepsis and septic shock, as defined by Sepsis-3 criteria, in whom test for thyroid function were performed" (line 101).

 

Comment 3: I suggest including the confidence interval for AUROC and the p-value of T4 in the multivariate model; differentiate the values ​​for the primary and secondary outcomes.

Response 3: The 95% CI for the AUROC of the multivariate models were added.

 

Comment 4: Introduction:  I only suggest that the authors evaluate maintaining the detailed description present in the fifth and sixth paragraphs.

Response 4: We have reduced the length of paragraph 5.

 

Comment 5: MATERIALS AND METHODS: partially adequate; include the STROBE; describe how APACHE and SOFA were obtained, whether directly from the patient's medical record/data or measured by the researchers and, if it was the first option, cite this as a probable limitation/measurement bias, due to the evaluation having been done by multiple professionals; describe the origin of the laboratory data: whether from hospital routine or specifically collected for the study; to describe the laboratory analysis techniques for these parameters in order to determine a reference/comparison standard for other studies; as well as how quality control was ensured, from sample collection to processing; to describe all the characterization and clinical variables that were investigated and how the data collection, cleaning, consistency, and validation process was carried out.

Response 5: We collected data from the hospital’s electronic records, including the SOFA and APACHE II scores within the first 24 hours, as declared in the Methods section: " We collected data from the hospital’s electronic records, as follows: age and sex of the patients, SOFA and APACHE II scores within the first 24 hours" (line 109). We added this limitation of the study in the discussion section: "Data was retrospectively retrieved from the patients' files, clinical scoring (SOFA and APACHE II) was performed by different physicians, during routine clinical care. Therefore, one of the limitations of this study might be the variability between healthcare professionals." (line 321). The laboratory technique used for measuring fT4 and TSH was added in the methods section, line 115: "Free thyroxine and TSH were measured using Electrochemiluminescence Immunoassay (ECLIA)." Another potential limitation, regarding the lack of standardization of patient selection for testing thyroid function, was highlighted in the discussions section, line 316: "Thyroid function was assessed upon clinical indication from the attending physician. A potential limitation would be the lack of a clear, systematic approach for selecting which patients would have fT4 and TSH measured, with possible inconsistencies between different physicians, and the relatively low proportion of patients where these parameters were available, out of all the septic patients admitted in the study period.".

 

Comment 6:  I suggest that in addition to what was done, the authors make a comparison between the TSH and T4 values ​​between survivors and non-survivors in each of the outcome scenarios, according to each comorbidity, so that we can see the relationship between them

Response 6: We have added in the discussion sections the following limitation: "Since many patients had several comorbidities and organ dysfunctions, intraclass assessment of differences would mean significant overlap between subgroups. Thus, we could not evaluate differences in mortality and thyroid hormone profiles between subgroups." (line 334)

 

Comment 7: The authors state that “APACHE II and SOFA scores, length of stay, and mortality were then compared between these three groups, and no significant difference was found between any of the parameters investigated (Table 4),” however, they present a p-value of 0.044 for 28-day mortality and 0.004 for hospital mortality: clarification is needed; The authors state that “The SOFA score had the best predictive ability, followed by the APACHE II score, for both primary and secondary outcomes,” however, according to Table 6, APACHE showed better prediction for 28-day mortality and SOFA for overall mortality: clarification is needed; what justified the authors using only age, hemoglobin, levels, fT4, and SOFA score for the multivariate analysis, given that the other parameters, except creatinine, were significant for the outcomes? Clarification is needed.

Response 7: We have made a mistake; the data displays clear differences in mortality between the 3 groups and we have corrected the interpretation in the main text (line 195). Thank you for pointing this mistake out. We have re-evaluated the interpretation for SOFA and APACHE II, and added in the text: "The SOFA and APACHE II score had similar predictive abilities, for both primary and secondary outcomes." (line 218). Variables used in the multivariate analysis were selected by the following considerations, specified in the discussion section, lines 297-303: "Variables included in the multivariate regression were selected based on their statistical significance in univariate analyses. Among severity scores, the SOFA score was favored over the simultaneous inclusion of SOFA and APACHE II, as these scores share overlapping components, and their combined use could reduce clinical relevance. Additionally, the SOFA score was preferred because it is included in the Sepsis-3 definition and offers greater practicality in routine clinical settings due to its simpler calculation.". We have tried several other combinations in the mutivariate analysis, but none had superior predictive value.

 

Comment 8: "I suggest that the authors dedicate one or two paragraphs to discussing the profile of their patients and whether these are similar to other profiles from Europe, Asia, Africa, and the Americas; I also suggest discussing the findings of comorbidities and how these influence or may be influenced by TSH and T4 dysfunctions.".

Response 8: To address this, we added the following statement in the discussion section: "The variability in the combination of different comorbidities in our single-center cohort, limits the generalizability of our results, and multicenter studies are required to confirm patients' profiles link to mortality." (line 337).

Thank you for all your comments. We have addressed all the required changes, and we believe that the quality of our manuscript has improved. Should there be any other requests, please let us know.  

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

Thank you for the opportunity to review your manuscript entitled   ,,Free thyroxine as a predictor of mortality in critically ill septic patients a seven-year, retrospective study”

I have carefully reviewed the manuscript. In the following, I provide my comments and recommendations in a structured, section by section manner, aiming to improve clarity, methodological rigor, and alignment between objectives, results, and conclusions.

Abstract

The mortality values in the abstract are not consistent with the mortality values in the Result section. They require alignment.

AUROC (fT4) is reported 0.779 in the abstract, and 0.799 in the text, possible editing error?

The number of patients included in the study is not presented in the abstract

No OR and 95% CI for fT4 are reported in the multivariate model.

 The conclusion must be formulated in a more cautious manner, given that it is a retrospective observational study.

Introduction

The following statement ,,Similar to global trends, recently indicated a progressive increase in sepsis incidence within Romanian medical centers, rising from 0.26% in 2007 to 2.85% in 2024", is not very clear. Is the term ,,incidence" probably misused?

The sections on the pathophysiology of the ESS are relatively extensive for a retrospective clinical trial, they should be reduced without losing coherence.

It should be explicitly clarified that the study is limited to fT4 because this is the biomarker systematically available in Romania.

The gap is suggested, but it is not clearly formulated and argued rigorously enough.

Beware of grammatical errors.

Replace the logistical justification ,,widely available,, with a scientific rationale linked to the identified knowledge gap.

Avoid vague expressions such as ,,local cohort,,  or “single-center Eastern European ICU cohort.

Material and method

Inconsistency regarding the research center in the Abstract: „tertiary ICU” and in Methods: „Anesthesia and Intensive Care I Department”

Confusers are presented incompletely, e.g. amiodarone, iodine, recent medication that affects protein binding (heparin, glucocorticoids, etc.)

You must explicitly mention in Methods if these therapies have been analyzed or declare as a limitation the lack of control for medications with endocrine impact, within the limits of the study.

To clarify:

1. How many sepsis/septic shock patients were hospitalized in total during the study period?
2. Have fT4 and TSH been systematically measured in all patients? Or only on clinical indication? And what were the criteria for testing?

Results

Mortality needs to be clarified, inconsistent with the abstract.

The hyperthyroid group has n=7, so any comparison with it is unstable and the p may be sensitive.

Avoid any conclusions about the hyperthyroid group, because no clinical conclusions can be drawn with 7 patients. A stratification into 2 groups: hypothyroid and non-hypothyroid would be more appropriate.

Discussions

The first part takes up almost descriptively the results already presented, the discussion should interpret, not repeat figures.

The claim that patients are in a ,,chronic phase of critical illness" is not proven by the study data.

Expand the limitations section with major methodological aspects.

Avoid extensive restatement of numerical results in the Discussion. Emphasize interpretation rather than repetition.

Consider expanding the Discussion to address the potential for personalized sepsis diagnosis and treatment, integrating emerging biomarkers beyond conventional measures. Recent evidence (e.g., DOI:10.3390/biom15111621) highlights novel immunometabolic and endothelial biomarkers that may help define sepsis subphenotypes, improve risk stratification, and guide targeted therapies. Discuss how these emerging markers compare with or complement fT4 in stratifying patients and predicting outcomes, and outline their potential implications for personalized clinical management in sepsis.

 

Author Response

Thank you very much for your comments on our manuscript. Please find below a point-by-point response to the requested changes:

Comment 1: Abstract: The mortality values in the abstract are not consistent with the mortality values in the Result section. They require alignment. AUROC (fT4) is reported 0.779 in the abstract, and 0.799 in the text, possible editing error? The number of patients included in the study is not presented in the abstract. No OR and 95% CI for fT4 are reported in the multivariate model. The conclusion must be formulated in a more cautious manner, given that it is a retrospective observational study.

Response 1: The mortality reported in the abstract is 28-day mortality (the primary outcome) for patients with sepsis, and septic shock, respectively. In the second paragraph of the results section, we have initially reported 28-day and in-hospital mortality for the entire patient cohort (sepsis and septic shock together). We have added the following statement to the results section for better clarity: "In the sepsis group, 28-day mortality was 29.73%, and 53.57% in the septic shock group." (line 150). We have modified the AUROC of fT4 in the abstract to the correct values of 0.799. Thank you for pointing out this mistake. We also included the number of patients analyzed in the abstract and altered the formulation of our conclusion. The OR (95% CI) for fT4 in the multivariate model was reported in Table 7: 0.2 (0.06 - 0.69) for 28-day mortality and 0.23 (0.07 - 0.78) for in-hospital mortality. We also added the 95% CI for the AUROC of the multiparametric models.

 

Comment 2: Introduction: The following statement ,,Similar to global trends, recently indicated a progressive increase in sepsis incidence within Romanian medical centers, rising from 0.26% in 2007 to 2.85% in 2024", is not very clear. Is the term ,,incidence" probably misused? The sections on the pathophysiology of the ESS are relatively extensive for a retrospective clinical trial, they should be reduced without losing coherence. It should be explicitly clarified that the study is limited to fT4 because this is the biomarker systematically available in Romania. The gap is suggested, but it is not clearly formulated and argued rigorously enough. Beware of grammatical errors. Replace the logistical justification ,,widely available ,,with a scientific rationale linked to the identified knowledge gap. Avoid vague expressions such as ,,local cohort,,  or “single-center Eastern European ICU cohort.

Response 2: We replaced the term "incidence" with "rates" for better clarity and reduced the section on the pathophysiology of ESS by shortening paragraph 5. We further clarified the fact that fT4 is the thyroid hormone fraction systematically available in Romania and replaced some of the vague terminology in the introduction section.

 

Comment 3: Inconsistency regarding the research center in the Abstract: „tertiary ICU” and in Methods: „Anesthesia and Intensive Care I Department”. Confusers are presented incompletely, e.g. amiodarone, iodine, recent medication that affects protein binding (heparin, glucocorticoids, etc.). You must explicitly mention in Methods if these therapies have been analyzed or declare as a limitation the lack of control for medications with endocrine impact, within the limits of the study. To clarify:

1. How many sepsis/septic shock patients were hospitalized in total during the study period?
2. Have fT4 and TSH been systematically measured in all patients? Or only on clinical indication? And what were the criteria for testing?

Response 3: We have modified the phrase "tertiary ICU" in the abstract with "the Anesthesia and Intensive Care I Department of the Cluj County Emergency Hospital, Cluj-Napoca, Romania".  We have added the following statement in the discussion sections, regarding medication administered during the ICU stay, which could potentially interfere with thyroid function: "Those receiving heparin or glucocorticoids during the ICU admission were also not excluded, but this does not alter the results of the study, since thyroid function was assessed early in the course of critical illness."(line 332). Regarding amiodarone therapy, we also mentioned in the original manuscript, in line 329, that:" patients receiving amiodarone therapy (either chronically or during their ICU stay) were not excluded". We added the total number of patients hospitalized with sepsis/septic shock in the results section (line 142): " During the study period, 1458 patients with sepsis and septic shock were admitted to our ICU." Regarding whether fT4 and TSH have been systematically measured, we added the following clarification is the discussion sections (line 316): "Thyroid function was assessed upon clinical indication from the attending physician. A potential limitation would be the lack of a clear, systematic approach for selecting which patients would have fT4 and TSH measured, with possible inconsistencies between different physicians, and the relatively low proportion of patients where these parameters were available, out of all the septic patients admitted in the study period."

 

Comment 4: Results Mortality needs to be clarified, inconsistent with the abstract. The hyperthyroid group has n=7, so any comparison with it is unstable and the p may be sensitive. Avoid any conclusions about the hyperthyroid group, because no clinical conclusions can be drawn with 7 patients. A stratification into 2 groups: hypothyroid and non-hypothyroid would be more appropriate.

Response 4: As previously explained in our response to Comment 1, the mortality reported in the abstract is 28-day mortality (the primary outcome) for patients with sepsis, and septic shock respectively. In the second paragraph of the results section, we have initially reported 28-day and in-hospital mortality for the entire cohort (sepsis and septic shock together). We have added the following statement to the results section for better clarity: "In the sepsis group, 28-day mortality was 29.73%, and 53.57% in the septic shock group." (line 150). Regarding the hyperthyroid group, we added the following clarification: "However, given the limited number of patients in the "Hyperthyroid" group (n=7), no clinical conclusion can be drawn regarding this group." (line 197). However, we still believe that stratifying the patients in 3 clear-cut groups, best describes patient's hormone profile, and might be relevant for larger, future studies.

 

Comment 5: The first part takes up almost descriptively the results already presented, the discussion should interpret, not repeat figures. The claim that patients are in a ,,chronic phase of critical illness" is not proven by the study data. Expand the limitations section with major methodological aspects. Avoid extensive restatement of numerical results in the Discussion. Emphasize interpretation rather than repetition.

Response 5: We have excluded the results from the discussion section, leaving only the interpretation in place, which allows comparisons with studies published by other authors. We have changed the phrase "chronic phase" to "more advanced phase of critical illness", due to delayed patient presentation. We have also expanded the limitation section.

Comment 6: Consider expanding the Discussion to address the potential for personalized sepsis diagnosis and treatment, integrating emerging biomarkers beyond conventional measures. Recent evidence (e.g., DOI:10.3390/biom15111621) highlights novel immunometabolic and endothelial biomarkers that may help define sepsis subphenotypes, improve risk stratification, and guide targeted therapies. Discuss how these emerging markers compare with or complement fT4 in stratifying patients and predicting outcomes, and outline their potential implications for personalized clinical management in sepsis.

Response 6: We incorporated the suggested reference, and added the following statement to the discussion sections (line 346): "Further research might include thyroid hormone profiles, together with novel biomarkers, such as micro ARN (miR) miR-122 and miR-150 and plasma gelsolin (pGSN), or others, to better define sepsis phenotypes, which might guide clinicians in tailoring a personalized treatment approach for each patient".

Thank you for all your comments. We have addressed all the required changes, and we believe that the quality of our manuscript has improved. Should there be any other requests, please let us know.  

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

Thank you for the revised version of your manuscript. The manuscript has been significantly improved, and only a minor clarification is required.

In the Conclusions section, you currently state that decreased fT4 levels are independently associated with increased mortality. Given the retrospective design and single center nature of the study, this statement should be explicitly limited to the studied population.

Please revise the sentence as follows:

,,Our research shows that decreased fT4 levels on ICU admission were independently associated with increased mortality in this cohort of septic patients,,

This modification will ensure appropriate scientific caution and avoid overgeneralization beyond the studied cohort.

 

Author Response

Thank you very much for your comments on our manuscript. Please find below our response to the requested change:

Comment 1: In the Conclusions section, you currently state that decreased fT4 levels are independently associated with increased mortality. Given the retrospective design and single center nature of the study, this statement should be explicitly limited to the studied population. Please revise the sentence as follows: ,,Our research shows that decreased fT4 levels on ICU admission were independently associated with increased mortality in this cohort of septic patients,,

Response 1: Thank you for pointing this mistake out. We have made the required change and revised our conclusion (line 339).

Thank you for comment. We have addressed the required change, and we believe that the quality of our manuscript has improved. Should there be any other requests, please let us know.