Transferrin saturation below 20 percent: what your result means

How it works

A transferrin saturation below 20 percent alongside a ferritin of 30 or more is consistent with iron deficiency even though the ferritin sits above the deficiency threshold, and this is the combination that is missed when only ferritin is read. Saturation measures how full the transport protein actually is, so it reflects the iron available to tissues right now, and BSG guidance regards it as more reliable than ferritin where inflammation is active, because inflammation inflates ferritin while saturation stays honest.

Guideline positions

BSG 2021 reads transferrin saturation alongside ferritin: a saturation below 20 percent alongside a ferritin of 30 or more is consistent with iron deficiency even where the ferritin looks acceptable, and saturation is more reliable than ferritin where inflammation is active. At the other end, the AASLD haemochromatosis guideline sets a saturation above 45 percent as the threshold for further evaluation, with EASL 2022 using above 45 percent for women and above 50 percent for men alongside a raised ferritin, and both advise confirming an elevated saturation with a second, fasting determination before anything else.

Practical framework

A saturation below 20 percent with symptoms suggests a GP conversation carrying both numbers, since the pair reads differently from either alone. A CRP alongside the two settles whether inflammation is distorting the ferritin. Where iron deficiency is confirmed and iron is appropriate, a retest around three months on shows whether the picture is repairing.

You can read your own numbers against these thresholds with the free blood test result interpreter on this site. It runs entirely on your device, nothing is saved, and pasting your report fills the values in for you.