Transferrin Saturation

Measured in %

The percentage of your blood's iron-carrying capacity that's actually filled — a calculated ratio, so it inherits the wobble of the two numbers behind it.

What it is

Transferrin saturation isn't measured directly; it's serum iron divided by TIBC, expressed as a percentage — roughly, how many of the iron 'bus seats' are occupied. Because it's built from two values that each move around (serum iron especially swings with time of day and recent intake), the ratio can vary meaningfully between draws. It's typically reviewed alongside ferritin and a blood count, and a fasting morning sample is often preferred when this number is the focus.

Typical range

  • Adults20–50 %

Source · Reference-lab convention (ARUP) (2024)

Reference ranges vary between laboratories, and what is normal for you depends on your own history. Your own lab’s range is the one printed on your report.

Worth asking your clinician

  • Was my sample taken in conditions that make this percentage reliable, or would a fasting morning draw be more informative?
  • How does my transferrin saturation fit with my ferritin and the rest of my iron results?
  • Is this something worth rechecking before we read anything into it?