Transferrin saturationNutrition library
LibraryBlood markersIron studies
Transferrin saturation
Transferrin saturation (TSAT) is the share of iron-binding sites occupied — the lab prints it, or we calculate it from the same draw.
Labs report TSAT as serum iron ÷ TIBC × 100. We do not catalog TIBC. When a date has serum iron (µmol/L) and transferrin (g/L) but no printed TSAT, the app estimates TIBC as transferrin × 25.1 and shows the same ratio, marked Calculated — it is not written as a logged lab. When the report also prints TSAT, that figure is used; 25.1 is a conversion, not that lab's TIBC assay.
How to read it
Display-only in Trends. Pair with ferritin (stores) and haemoglobin. A calculated value is for the same-day iron studies only — log the printed TSAT when the report includes it.
Trimester context
| Stage | For the mother | For the baby |
|---|---|---|
| First trimester | — | — |
| Second trimester | Saturation often falls as transferrin rises and stores are drawn down. | Placental iron transfer depends on maternal circulating supply. |
| Third trimester | Low saturation with low ferritin supports iron-deficiency workup before delivery. | Late accretion is highest — circulating supply still matters. |