Is iron saturation the same as transferrin saturation?

Iron Saturation and Transferrin Saturation: Terminology Clarification

Yes, "iron saturation" and "transferrin saturation" (TSAT) refer to the same laboratory measurement—they are interchangeable terms for the percentage of transferrin's iron-binding sites that are occupied by iron. 1

Definition and Calculation

• Transferrin saturation is calculated as: TSAT (%) = (serum iron / TIBC) × 100, where TIBC represents total iron-binding capacity. 1

• The transferrin molecule contains two binding sites for transporting iron, and a TSAT of 50% indicates that half of these binding sites are occupied by iron. 2

• TIBC measures the iron-binding capacity within serum and reflects the availability of iron-binding sites on transferrin. 1, 3

Clinical Interpretation

• Normal TSAT range in adults is typically 20-50%. 1

• Low TSAT (<20%) indicates a high proportion of vacant iron-binding sites and is commonly used to confirm iron deficiency. 1, 3

• In healthy individuals without inflammation, TSAT below 16% indicates absolute iron deficiency. 1

• In patients with chronic inflammatory conditions (heart failure, chronic kidney disease, inflammatory bowel disease), TSAT <20% is the diagnostic threshold. 1

• High TSAT (>50%) may indicate iron overload conditions. 1

Important Clinical Caveats

• TSAT has significant diurnal variation—levels rise in the morning and fall at night—so serial measurements should be obtained at consistent times. 2, 1

• Recent meals increase serum iron concentration and affect TSAT measurements. 1

• Inflammation and infection can decrease serum iron concentration, artificially lowering TSAT despite adequate iron stores. 1

• Day-to-day variation is greater for TSAT than for hemoglobin, making single measurements less reliable than serial assessments. 1

Functional vs. Absolute Iron Deficiency

• Functional iron deficiency can occur despite normal or elevated ferritin levels, particularly when erythropoiesis is pharmacologically stimulated. 2

• In functional iron deficiency, TSAT decreases to <20% even with adequate iron stores (ferritin 100-700 ng/mL), because iron cannot be mobilized quickly enough to meet increased demand. 2

• This contrasts with absolute iron deficiency, where both TSAT (<20%) and ferritin (<100 ng/mL in chronic kidney disease patients) are low. 2

Timing of Laboratory Assessment

• Iron parameters should not be evaluated within 4 weeks of total dose iron infusion, as circulating iron interferes with the assay. 1

• Laboratory evaluation following IV iron should include CBC and iron parameters (ferritin, TSAT) 4 to 8 weeks after the last infusion. 1