No obvious association exists between red blood cell distribution width and thyroid function.

We aimed to explore gender impacts on the associations between red blood cell distribution width (RDW) and thyroid function in the Chinese population. Gender impacts on the associations between RDW and thyroid function in 8424 males and 5198 females were investigated. RDW was found significantly lower in males than in females. An increasing trend of RDW along with aging was demonstrated in males. For females, an obvious decrease was shown during menopause period. From binary logistic regression, RDW displayed negative relationship with hypothyroidism in both genders as a single factor. However, if RDW was analyzed as a categorical variable (in RDW width quartiles) and as a continuous variable in models with covariates, all the odds ratios were negative, except for a weak-negative relationship with hypothyroidism in women in a continuous RDW model. The current study suggests that anisocytosis could be a contributing factor in thyroid dysfunction.