To investigate the association between blood routine (BRT) parameters and bone loss as well as the possible mechanism of this association with bone loss in the middle- aged and elderly patients.

A total of nine hundred and ninety-eight subjects (the total) aged≥40 years in General Hospital of Southern Theater Command of People's Liberation Army from March 2015 to January 2018 were enrolled in a cross-sectional studyPatients were divided into two groups as “at least osteopenia group” (including osteopenia, osteoporosis, and severe osteoporosis) and “normal group” according to the diagnosis standard of OP. The above indicators were analyzed and compared between the two groups. Binary multivariate logistic regression analysis was carried out to explore the association between BRT parameters and risk of bone loss in the subjects Mediation Effect was conducted to test endocrine variables as mediators in the correlation of BRT parameters with the bone loss for the possible mechanisms.

There were 669 cases in the at least osteopenia group and 329 in the normal group. RBC, Hb, HCT and MCHC were all positively correlated with BMD of lumbar spine(L1-4), left femoral neck and left femur, along with lymph positively correlated with BMD of left femoral neck and left femur, respectively. Eosinophils(Eo) was positively correlated with BMD of L1-L4 and RDW-SD together with RDW-CV were both negatively correlated with BMD of left femoral neck and left femur. By binary multivariate logistic regression, only Hb was associated with bone loss and the OR value was 0.478 as protective factor for BMD. Estradiol (E₂) and testosterone (T) had partial mediating effect on the association of BRT parameters with the risk of bone loss. The mediating effect of E₂ on the relationship between WBC and bone loss accounted for 46.35% of the total effect, and that of T on the relationship between RBC, Hb, HCT, MCHC and bone loss accounted for 27%, 18.3%, 31.1% and 26.8%, respectively.

Bone loss in the middle-aged and elderly population is accompanied with the change of BRT parameters and the erythrocyte indices tend to be more obvious especially the Hb, which indicates anemia had a potential connection with bone loss. Sex hormone, especially T, is an important mediating variable in the association between blood routine parameters and bone loss.