Transferrin Saturation Calculator
Transferrin saturation (TSAT) from serum iron with TIBC, UIBC or transferrin (µg/dL or µmol/L; mg/dL or g/L) — with interpretation for iron deficiency (< 16–20%) and overload (> 45%), a ferritin pattern adjusted for inflammation and sex, and the heart-failure (ESC) and CKD (KDIGO 2026) iron criteria.
How it works
TSAT (%) = serum iron ÷ TIBC × 100 · TIBC = serum iron + UIBC · TIBC (µg/dL) ≈ transferrin (mg/dL) × 1.389 (or 1.41 / 1.25) · µmol/L × 5.585 = µg/dL · ferritin pmol/L × 0.445 = µg/L
Transferrin is the protein that carries iron in plasma, and its saturation measures what fraction of its binding sites hold iron. Labs report the binding side in different ways — as TIBC, as UIBC (the empty sites, so TIBC = iron + UIBC) or as transferrin itself, which converts to TIBC because each molecule binds two iron atoms (about 1.39 µg of iron per mg of transferrin). In iron deficiency the liver makes more transferrin while serum iron falls, so saturation drops below 16–20%, often before haemoglobin does. Inflammation lowers transferrin and raises ferritin, which hides deficiency: that is why ferritin under 30 µg/L normally confirms low stores, but up to 100 µg/L can still mean deficiency when inflammation is present, and why heart-failure guidelines (ESC) define iron deficiency as ferritin under 100, or 100–299 with saturation under 20%. The 2026 KDIGO kidney guideline starts iron in haemodialysis patients with ferritin ≤ 500 µg/L and saturation ≤ 30%, and in other CKD patients with ferritin under 100 and saturation under 40%, or ferritin 100–299 and saturation under 25%; iron is withheld above ferritin 700 or saturation 40%. At the other end, a fasting saturation above 45% is the most sensitive early sign of hereditary haemochromatosis, and with ferritin over 200 µg/L in women or 300 µg/L in men it prompts HFE genotyping.
Worked example
Serum iron 45 µg/dL and TIBC 420 µg/dL: saturation 45 ÷ 420 × 100 = 10.7% — low; UIBC 375 µg/dL. With ferritin 12 µg/L this is absolute iron deficiency. A heart-failure patient with iron 60 µg/dL, transferrin 250 mg/dL and ferritin 180 µg/L: TIBC 250 × 1.389 = 347 µg/dL, saturation 17.3%, which meets the ESC definition of iron deficiency even though ferritin is in the normal range.
Sources: Eleftheriadis T et al. Which is the best way for estimating transferrin saturation? Ren Fail 2010 (PMID 20722575) · WHO 2020 guideline on use of ferritin concentrations to assess iron status in individuals and populations · McDonagh TA et al. 2021 ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure (iron deficiency definition) · KDIGO 2026 Clinical Practice Guideline for Anemia in CKD — key takeaways (iron thresholds) · EASL Clinical Practice Guidelines on haemochromatosis · Medscape — Transferrin Saturation: Reference Range, Interpretation
Frequently asked questions
Should I stop iron tablets before the test?
Yes — oral iron raises serum iron for many hours. Hold supplements for at least 24 hours and take a morning fasting sample.
My lab gives UIBC, not TIBC. What do I enter?
Choose UIBC: the calculator adds serum iron and UIBC to get TIBC, then divides. For example iron 45 and UIBC 375 give TIBC 420 and a saturation of 10.7%.
What saturation qualifies for IV iron in heart failure or CKD?
The ESC heart-failure guideline defines iron deficiency as ferritin under 100 µg/L, or 100–299 µg/L with saturation under 20%. KDIGO 2026 starts iron on haemodialysis when ferritin is 500 µg/L or less and saturation 30% or less; without dialysis (or on peritoneal dialysis) when ferritin is under 100 with saturation under 40%, or 100–299 with saturation under 25%. Choose the condition under “More options” to check these criteria; the treatment decision rests with the clinician.
Why does inflammation change the ferritin cut-off?
Ferritin is an acute-phase protein, so infection, inflammation or liver disease raise it even when iron stores are low. Without inflammation, ferritin under 30 µg/L indicates deficiency; with inflammation, up to 100 µg/L can still be compatible with it.
What saturation suggests haemochromatosis?
A fasting saturation above 45% is the usual screening threshold. Together with ferritin above 200 µg/L in women or 300 µg/L in men, it leads to HFE genotyping.
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Clinical decision tool for education and for use by trained clinicians alongside judgement — not a diagnosis and not a substitute for medical assessment. Scores validated in specific populations may not apply to every patient.