TFRC and Iron deficiency anemia: In addition to serum ferritin, outcome measures relating to iron status that were included in our meta-analyses included hemoglobin, hematocrit, iron deficiency (measured by plasma ferritin concentration <12 μg/L), iron deficiency anemia (measured by hemoglobin <11 g/dL and plasma ferritin <12 μg/L), serum iron concentration, and sTfR.