TF and heart failure: ID has been defined in various ways (as defined by heart failure guideline criteria: ferritin <100 ng/ml or, when 100–299 ng/ml, a transferrin saturation (TSAT) <20%; ferritin <15 ng/ml; ferritin <30 ng/ml; ferritin <100 ng/ml; TSAT <20%; or serum iron <13 μmol/L) (1, 14), prior research has primarily examined the association between isolated or a few definitions of ID and mortality.