Transferrin saturation (TSAT) is a reliable marker of iron status in a patients body. It is the ratio of serum iron (SE) and total iron-binding capacity, multiplied by 100. It is a clinical practice of checking the iron status of a patient. Given here is the transferrin serum iron saturation formula for calculating the TSAT value, with the normal reference ranges. For instance, a value of 15% means that 15% of iron-binding sites of transferrin are being occupied by iron.