Transferrin Saturation (TSAT) Calculator — Iron Metabolism Assessment
Transferrin saturation (TSAT) is a key laboratory value that measures the percentage of iron-binding sites on transferrin that are occupied by iron. It is essential for diagnosing and monitoring iron deficiency, iron overload, and guiding iron replacement therapy.
About
Transferrin saturation (TSAT) is the ratio of serum iron to total iron-binding capacity (TIBC), expressed as a percentage. TSAT is a dynamic measure of iron availability for erythropoiesis. It falls early in iron deficiency, often before anemia develops, making it a sensitive screening test. It rises in iron overload conditions such as hereditary hemochromatosis and transfusion-related hemosiderosis. TSAT can be calculated using either directly measured TIBC or calculated from transferrin concentration (TIBC = transferrin × 1.25). The normal range is 16-50%. Values <16% suggest iron deficiency, while values >50% suggest iron overload. TSAT is typically interpreted alongside serum ferritin, as ferritin reflects iron stores while TSAT reflects iron supply.
Formula
TSAT (%) = (Serum Iron / TIBC) × 100 If TIBC not available: TIBC = Transferrin (mg/dL) × 1.25
Transferrin saturation is calculated by dividing serum iron by total iron-binding capacity (TIBC) and multiplying by 100. If TIBC is not directly measured, it can be estimated from transferrin: TIBC (μg/dL) = transferrin (mg/dL) × 1.25. TSAT <16% indicates inadequate iron supply for erythropoiesis (iron deficiency). TSAT >50% suggests iron overload. In iron deficiency, TSAT falls early (before ferritin drops in some cases). In inflammation, both iron and TIBC decrease, potentially maintaining a normal TSAT despite functional iron deficiency.
Score Interpretation
TSAT is a critical parameter in the diagnosis and management of iron disorders. In chronic kidney disease, TSAT is used alongside ferritin to guide iron replacement therapy and ESA (erythropoiesis-stimulating agent) dosing. A TSAT <20% with ferritin <100 ng/mL in CKD patients typically warrants iron supplementation. In hereditary hemochromatosis, TSAT is the earliest abnormal laboratory finding, often exceeding 45% in men and 40% in women before ferritin rises. TSAT is also used to monitor therapeutic phlebotomy efficacy.
Iron Deficiency — 0–15.99
TSAT <16%. Indicates inadequate iron supply for erythropoiesis.
Management: Evaluate for iron deficiency. Check ferritin, iron studies, CBC. Consider oral or IV iron supplementation.
Normal — 16–50
TSAT 16-50%. Adequate iron supply for erythropoiesis.
Management: No iron replacement needed based on TSAT alone.
Iron Overload — 50.01+
TSAT >50%. Suggests iron overload. Evaluate for hemochromatosis.
Management: Perform iron studies including ferritin. Consider HFE genetic testing for hereditary hemochromatosis.
Reference Ranges
| Population | Normal Range | Notes |
|---|---|---|
| Healthy adults | 16 - 50% | TSAT may be lower in women of reproductive age due to menstrual loss |
| CKD patients on dialysis | 20 - 50% (target for iron therapy) | KDIGO guidelines recommend maintaining TSAT >20% in CKD patients on ESA therapy |
Dr. Khaled Hassan
Dr. Khaled is a cardiology consultant with experience in acute cardiac care.
View medical review board & editorial policy →Example Calculation
A 68-year-old woman with chronic kidney disease presents with fatigue. Serum iron 35 μg/dL, TIBC 280 μg/dL. TSAT = (35/280) × 100 = 12.5%. This low TSAT (<16%) indicates iron deficiency. She is started on IV iron sucrose with improvement in her energy levels over 4 weeks.
Related Conditions
Related Medications
Common Mistakes
Interpreting TSAT without ferritin
TSAT reflects iron supply while ferritin reflects iron stores. Both are needed for a complete picture of iron status. In inflammation, ferritin is elevated (acute phase reactant) and TSAT may be low (functional iron deficiency).
Frequently Asked Questions
Can TSAT be normal in iron deficiency?
How often should TSAT be monitored in CKD patients?
References
- Camaschella C. Iron deficiency. Blood. 2019;133(1):30-39. PubMed
- KDIGO Clinical Practice Guideline for Anemia in Chronic Kidney Disease. Kidney Int Suppl. 2012;2(4):279-335.