Association between red blood cell distribution width and in-ICU mortality in asthmatic patients: A cohort study

<bold>Background:</bold> Red blood cell distribution width (RDW) has been shown to be associated with elevated mortality risk in a wide range of diseases. However, limited data are available for critically ill patients with asthma. <bold>Methods:</bold> Data for all 4003 asthmatic patients were extracted from the MIMIC-IV database. A multivariate Cox proportional hazards regression model was used to assess the correlation between RDW and in-ICU mortality in asthmatics. Restricted cubic splines (RCS) and a threshold effect model were employed to observe whether there was a nonlinear relationship between RDW and in-ICU mortality in asthmatics. <bold>Results:</bold> A total of 169/4003 patients died. RDW was positively associated with in-ICU mortality (HR(95% CI) 1.03(1.03–1.16); p =0.0033) after adjusting for confounders. The RCS revealed a non-linear relationship between RDW and in-ICU mortality (p value for nonlinearity<0.05). A two-piecewise regression model was used to obtain a threshold inflection point value of 18. The HR and 95%CI on the left inflection point were 1.30 and 1.16-1.45(p<0.0001); on the right inflection point, they were 0.92 and 0.80-1.05(p = 0.1997). Subgroup analysis indicated that interaction effects might exist between gender, RDW, and in-ICU mortality. The risk of in-ICU mortality was lower for asthmatic adults with a low RDW tertile, compared with asthmatics with middle and high RDW tertiles, by Kaplan-Meier analysis. <bold>Conclusions:</bold> RDW might be an independent predictor of in-ICU death risk in asthmatics. The relationship between RDW and in-ICU mortality in asthmatics was nonlinear. RDW values and in-ICU mortality were positively correlated when the RDW value was 18%.