Reference interval of monocyte distribution width (MDW) in healthy blood donors

Background: The aim of the study was to accurately establish the reference interval (RI) of monocyte distribution width (MDW) in healthy blood donors by the direct method using different statistical approaches. Methods: MDW was measured in 486 subjects. RI of MDW was calculated by the non-parametric method, the robust method and, the Harrell-Davis bootstrap method and using different tests to identify potential outliers (Dixon-Reed and Tukey). Results: Lower and upper reference limits of the RI calculated by the non-parametric method were, 16.22 (90%CI 15.78–16.47) – 23.15 (90%CI 22.80–24.10) (without outlier removal), and 16.44 (90%CI 16.21–16.67) – 22.99 (90%CI 22.33–23.22) (after outlier removal). The RIs based on the robust method were, respectively, 16.29–22.98 (without) and 16.50–22.67 (with outlier removal). Finally, the RIs calculated by the Harrell-Davis bootstrap method, without or after outlier removal, were 16.19–23.24 and 16.43–22.93. Thus, the RIs obtained by the three calculation methods were very similar. Additionally, no RI partition was done since no significant gender or age association was found. Conclusions: Our results support the use of a unique RI of MDW, independently of sex and age.