Transferrin Saturation
Percentage of iron-loaded transferrin – key value for iron status and hemochromatosis
Also known as
Definition
Transferrin saturation (TS, also transferrin saturation index or TSAT) indicates what proportion of available transferrin is actually loaded with iron. It is calculated as serum iron divided by total iron-binding capacity (TIBC) × 100. Together with ferritin, it is the key parameter for differentiating iron deficiency (low TS) from iron overload (high TS, suspected hemochromatosis).
| Parameter | Value |
|---|---|
| Unit | % |
| Reference Range | 20–45% | Women tend toward the lower end (15–35%) |
Agree on your personal target range with your doctor.
↓ What a low value means
Low transferrin saturation (< 16%) is a sensitive marker for iron-deficient erythropoiesis — the bone marrow is not receiving enough iron for hemoglobin synthesis, even before hemoglobin falls. Combined with low ferritin, it confirms the iron deficiency diagnosis. TS 16–20% with normal ferritin: gray zone — functional iron deficiency possible.
↑ What a high value means
Elevated transferrin saturation (> 45%) is suspicious for iron overload. If ferritin is also elevated, a genetic hemochromatosis workup (HFE gene test) may follow; your doctor decides whether it is ordered. Secondary causes: frequent transfusions, sideroblastic anemia, dyserythropoietic anemias.
✓ What can influence this value
Transferrin saturation is influenced by iron intake and iron supplements, absorption disorders in the intestine, blood loss, inflammation, liver disease, and hereditary iron storage diseases such as hemochromatosis. Vitamin C in a meal can increase iron absorption. Serum iron varies over the course of the day and is changed by iron supplements taken shortly before, which affects the measurement. The assessment is made by the treating doctor.
When to test
Transferrin saturation is usually measured together with ferritin, serum iron, transferrin, and a complete blood count, for example when investigating anemia or when hemochromatosis is suspected, including in first-degree relatives of people affected. Because serum iron varies over the day, the measurement is preferably done fasting.
Frequently asked questions
Why are serum iron, transferrin, and ferritin measured together? +
Each parameter measures something different: ferritin reflects iron stores (distorted by inflammation), transferrin shows transport capacity, serum iron the currently circulating amount. Transferrin saturation links serum iron with capacity. Only together do they allow differentiation of iron deficiency, inflammatory anemia, and iron overload.
Why is transferrin saturation usually measured fasting? +
Serum iron is subject to strong daily variation (rises up to 30% after meals, circadian rhythm peaking in the morning). Transferrin saturation is calculated from serum iron and therefore fluctuates equally. Morning fasting measurement ensures comparability.
What is hereditary hemochromatosis and how is it detected? +
Hereditary hemochromatosis (HFE mutation, especially C282Y homozygosity) is the most common genetic iron overload disease in Northern Europe. First finding: transferrin saturation > 45–55%, often before ferritin rises. Confirmed by HFE gene test. Early symptoms: fatigue, joint pain; late complications: liver cirrhosis, diabetes, heart disease.
Transferrin Saturation
Sources
Last updated: May 28, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.