Are TSAT and Iron Saturation Percentage the Same?
Yes, TSAT (Transferrin Saturation) and iron saturation percentage are the same measurement—they both refer to the percentage of transferrin binding sites occupied by iron, calculated as serum iron divided by total iron binding capacity (TIBC) and multiplied by 100. 1
Understanding the Terminology
TSAT is simply the abbreviated term for "transferrin saturation," which is expressed as a percentage and represents the proportion of transferrin molecules that are saturated with iron 1
The calculation is identical regardless of which term is used: percent TSAT = (serum iron × 100) ÷ TIBC, where TIBC essentially measures circulating transferrin 1
Both terms describe the same physiologic concept: the transferrin molecule contains two binding sites for transporting iron from storage sites to erythroid progenitor cells, and a TSAT of 50% indicates that half of these binding sites are occupied by iron 1
Clinical Context and Interpretation
TSAT reflects iron that is readily available for erythropoiesis, distinguishing it from ferritin which reflects storage iron in the liver, spleen, and bone marrow 1
In clinical practice, TSAT <20% has traditionally been used to indicate iron deficiency, though this threshold varies by clinical context (e.g., <16% in healthy subjects, <20% in CKD patients) 1
The European Association for the Study of the Liver defines elevated TSAT as >45% when evaluating for hemochromatosis, demonstrating that the same measurement is used across different iron metabolism disorders 1
Important Clinical Caveats
TSAT shows diurnal variation due to fluctuations in serum iron levels, but serial measurements obtained at the same time of day (such as during clinic or dialysis visits) minimize this variability 1
TSAT should not be measured within 4 weeks of intravenous iron administration, as circulating iron interferes with the assay and produces spurious results 1
Low TSAT (<20%) with normal or elevated ferritin indicates functional iron deficiency, where iron stores exist but cannot be mobilized quickly enough to support erythropoiesis 1