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ABO Blood Type and ARDSABO Blood Type and ARDS FREE TO VIEW

Yiqiang Zhan, MD
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From the Department of Medical Epidemiology and Biostatistics, Karolinska Institutet.

CORRESPONDENCE TO: Yiqiang Zhan, MD, Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Nobels väg 12A, Stockholm, Sweden 17177; e-mail: yiqiang.zhan@ki.se


FINANCIAL/NONFINANCIAL DISCLOSURES: The author has reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2015;147(2):e67. doi:10.1378/chest.14-2491
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To the Editor:

I read with great interest the article by Reilly et al1 in a recent issue of CHEST (April 2014). In this article, the authors prospectively studied the association of ABO blood types with ARDS risk in patients with major trauma and severe sepsis. The results were very interesting; however, a few pertinent points should be analyzed before these results are accepted into clinical practice.

First, the authors did not hypothesize that sex may modify the association between ABO blood type and ARDS risk. Previous studies found that women were more likely to develop ARDS compared with men,2 whereas sex is not associated with ABO blood type distribution. Thus, it might be reasonable to hypothesize that the effects of ABO blood type on ARDS differ between men and women. Because the authors had these data, more input could have been gained by carrying out additional analysis to investigate whether sex is an effect modifier.

Second, because the study used a prospective study design, which meant that the interested outcome (ARDS) occurred after the exposure, relative risk should have been reported using log-linear regression models rather than the reported OR by logistic regression models.3 Although an OR can be converted to relative risk, it may have been more informative and intuitive to report relative risk for this prospective study.

Last, the author considered diabetes, alcohol use, and chronic heart failure, among others, as potential confounders in the multivariable models. However, several criteria should be met for a variable to be identified as a potential confounder. One of the criteria is that the potential variable should not be in the pathway between exposure (ABO blood type) and outcome (ARDS). If it is in the pathway, this variable should be considered as a mediator, which cannot be adjusted in the models when total effect (direct and indirect effect) of ABO blood type on ARDS is the main research question. In this study, some variables, such as diabetes and chronic heart failure,4 may lie in the pathway between ABO blood type and ARDS, so they should not be adjusted in the final analysis. The authors can choose to draw a directed acyclic graph5 to select which variables should be included in the models. I anticipate that the effect of ABO blood type on ARDS would be stronger than reported in the article.

References

Reilly JP, Meyer NJ, Shashaty MGS, et al. ABO blood type A is associated with increased risk of ARDS in whites following both major trauma and severe sepsis. Chest. 2014;145(4):753-761. [CrossRef] [PubMed]
 
Heffernan DS, Dossett LA, Lightfoot MA, et al. Gender and acute respiratory distress syndrome in critically injured adults: a prospective study. J Trauma. 2011;71(4):878-883. [CrossRef] [PubMed]
 
Symons MJ, Moore DT. Hazard rate ratio and prospective epidemiological studies. J Clin Epidemiol. 2002;55(9):893-899. [CrossRef] [PubMed]
 
He M, Wolpin B, Rexrode K, et al. ABO blood group and risk of coronary heart disease in two prospective cohort studies. Arterioscler Thromb Vasc Biol. 2012;32(9):2314-2320. [CrossRef] [PubMed]
 
Textor J, Hardt J, Knüppel S. DAGitty: a graphical tool for analyzing causal diagrams. Epidemiology. 2011;22(5):745. [CrossRef] [PubMed]
 

Figures

Tables

References

Reilly JP, Meyer NJ, Shashaty MGS, et al. ABO blood type A is associated with increased risk of ARDS in whites following both major trauma and severe sepsis. Chest. 2014;145(4):753-761. [CrossRef] [PubMed]
 
Heffernan DS, Dossett LA, Lightfoot MA, et al. Gender and acute respiratory distress syndrome in critically injured adults: a prospective study. J Trauma. 2011;71(4):878-883. [CrossRef] [PubMed]
 
Symons MJ, Moore DT. Hazard rate ratio and prospective epidemiological studies. J Clin Epidemiol. 2002;55(9):893-899. [CrossRef] [PubMed]
 
He M, Wolpin B, Rexrode K, et al. ABO blood group and risk of coronary heart disease in two prospective cohort studies. Arterioscler Thromb Vasc Biol. 2012;32(9):2314-2320. [CrossRef] [PubMed]
 
Textor J, Hardt J, Knüppel S. DAGitty: a graphical tool for analyzing causal diagrams. Epidemiology. 2011;22(5):745. [CrossRef] [PubMed]
 
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