TF and chronic kidney disease: In normal healthy individuals, iron deficiency (ID) is defined as transferrin saturation (TSAT) < 16% and serum ferritin < 30 μg/L [1], but in people with chronic kidney disease (CKD), defined thresholds for iron deficiency are higher (ferritin < 100 μg/L or TSAT < 20%), albeit this not evidence-based.