Effect of age and gender on reference intervals of red blood cell distribution width (RDW) and mean red cell volume (MCV).

Background: Red blood cell distribution width (RDW) was recently shown to be age-dependent when using Sysmex XE-2100 hematology analyzers. As measuring RDW is subject to technology, we have investigated if this relation also exists when using a different hematology analyzer, Abbott CELL-DYN Sapphire. In addition, as RDW is generally expressed relative to mean red blood cell volume (MCV), we have explored how MCV influences the age-dependency of RDW.

Methods: We measured RDW and MCV in a large cohort and calculated RDW-SD (the "absolute" RDW), which does not contain MCV. For establishing reference intervals we used Bhattacharya statistics.

Results: In our study cohort of 8089 individuals we found a strong association between RDW and age, but not with gender. Also MCV showed an age-related increase over the entire age range. The conventional RDW increased by 6% from the youngest to oldest age class, whereas RDW-SD increased by nearly 15%. This difference was caused by a mean age-related increase in MCV of 6.6%. Age-dependent reference intervals were established for RDW, RDW-SD and MCV.

Conclusions: The age-dependency of RDW seems to be a universal biological feature rather than related with a single type of hematology analyzer. As not only RDW, but also MCV increases with age, we propose that future studies on the prognostic significance of RDW take its age-dependency into account and focus on RDW-SD as a potential marker of adverse events in many clinical conditions.