# Transferrin saturation

Transferrin saturation (TSAT) is the share of iron-binding seats on transferrin, your blood's main iron-carrier, that are filled with iron. You calculate it as (serum iron ÷ total iron-binding capacity) × 100. Normally, transferrin is 20 to 35% saturated, leaving spare capacity to soak up loose iron. The normal range is about 15 to 50% in adults, and values below 20% point to iron deficiency. When TSAT climbs above 45 to 50%, a dangerous form of iron (non-transferrin-bound iron, or NTBI) shows up in your plasma. It builds up in your liver, heart, and hormone glands. There it drives free-radical reactions, fat oxidation, and a form of cell death called ferroptosis. Chronically high TSAT is linked to higher all-cause death. A NHANES I follow-up (n = 10,714; Mainous et al., 2004) found a hazard ratio of 1.60 (95% CI 1.17 to 2.21) for TSAT above 55%. A NHANES II analysis by the same group found that high TSAT plus high dietary iron roughly tripled the death risk (HR 2.90; 95% CI 1.39 to 6.04). A fasting TSAT above 45% is the standard first screen for hereditary hemochromatosis (usually HFE C282Y homozygosity). The EASL 2022 guidelines define iron overload as TSAT above 45% plus ferritin above 200 µg/L in women, or TSAT above 50% plus ferritin above 300 µg/L in men, with HFE gene testing once either is confirmed. Because TSAT reflects iron flow rather than total stores, it complements ferritin and can catch early iron excess before organ damage shows up.

## Sources

- Mainous AG, Gill JM, Carek PJ. (2004). Elevated serum transferrin saturation and mortality. Annals of Family Medicine. https://doi.org/10.1370/afm.25
- Mainous AG, Wells B, Carek PJ, Gill JM, Geesey ME. (2004). The mortality risk of elevated serum transferrin saturation and consumption of dietary iron. Annals of Family Medicine. https://doi.org/10.1370/afm.82
- Zoller H, Schaefer B, Vanclooster A, et al.. (2022). EASL Clinical Practice Guidelines on haemochromatosis. Journal of Hepatology. https://doi.org/10.1016/j.jhep.2022.03.033

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_Canonical: https://longevity-switzerland.com/en/glossary/transferrin-saturation · Part of Longevity Cities · Updated 2026-06-22_