Circulating serum iron: fluctuates through the day and with meals.
What it is
Serum iron in µmol/L. Morning fasting samples are preferred when iron studies are performed. Iron alone is a poor iron-status test.
Serum iron measures iron bound to transferrin in plasma at one moment in time. It swings with the clock, recent meals, inflammation, and supplements. Morning fasting samples are preferred when iron studies are formally requested.
Why it matters
Ferritin, transferrin saturation, and the blood count give a clearer picture. Diurnal variation and recent meals swing serum iron widely.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
Serum iron alone cannot diagnose iron deficiency or overload. Ferritin (stores), transferrin saturation, and the FBC tell the story. A low afternoon iron after a meal skip means little; a low ferritin with microcytosis means more.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
How it affects the body
Serum iron reflects iron bound to transferrin in transit to marrow and tissues, a snapshot, not stores.
Transferrin delivers iron to marrow erythroblasts via transferrin receptors. When delivery falters, haemoglobin synthesis slows. Inflammation up-regulates hepcidin, trapping iron in stores and lowering serum iron even when ferritin is not low.
For athletes
Athletes should prioritise ferritin and full iron studies over isolated serum iron when investigating fatigue or “sports anaemia”.
Request a proper iron panel (ferritin ± saturation) for athlete fatigue work-ups. Avoid high-dose iron within a day of blood draw if you want a clean serum iron, and never supplement high-dose iron without confirming need.
