About transferrin saturation
Transferrin saturation (TSAT) is a laboratory measure of how much of the body's iron-carrying capacity is currently occupied by iron. Transferrin is the blood protein that shuttles iron between the gut, storage sites, and the bone marrow. Rather than measuring transferrin directly, most labs report two related values — serum iron and total iron-binding capacity (TIBC) — and TSAT is calculated as the ratio between them.
The standard formula
TSAT (%) = (serum iron ÷ TIBC) × 100. Serum iron is the amount of iron currently circulating in the blood, bound to transferrin. TIBC is a measure of the total amount of iron the available transferrin could carry if it were fully saturated. Dividing one by the other and multiplying by 100 gives the percentage of binding sites currently in use. Because TSAT is a ratio, the result is the same whether both inputs are measured in µg/dL or µmol/L, as long as both use the same unit.
Reading UIBC alongside TSAT
Unsaturated iron-binding capacity (UIBC) is simply TIBC minus serum iron — the portion of binding capacity not currently carrying iron. Serum iron, UIBC, and TIBC always satisfy serum iron + UIBC = TIBC, so knowing any two lets you derive the third.
Putting the result in context
A commonly cited adult reference range for TSAT is roughly 20% to 50%, though the precise interval varies by laboratory and testing method. Values persistently below about 15-20% are often seen with iron deficiency, while values above roughly 45-50% can point toward iron overload conditions such as hereditary hemochromatosis. A single measurement can be affected by recent meals, supplements, time of day, and inflammation, so isolated results are typically interpreted alongside other iron studies (ferritin, hemoglobin) rather than on their own.
When to consult a professional
This calculator performs the standard TSAT arithmetic; it does not diagnose iron deficiency, iron overload, or any other condition. For any result outside the typical range, or for decisions about supplementation or treatment, consult a licensed healthcare provider who can interpret the number alongside your full iron panel and clinical history.