Iron

What is Iron?

Iron carries oxygen and fuels your energy production. It's the raw material your body builds haemoglobin from: a single measurement that shifts with the day and your last meal. Enough iron supports your energy, your concentration and the production of red blood cells.

Clinical frame

Serum iron measures only the transport compartment: the iron circulating bound to transferrin, as a snapshot of supply and uptake, mainly by the bone marrow. It is not a measure of stores and must never be interpreted on its own ^[1].

The value fluctuates strongly for reasons unrelated to stores: a circadian rhythm with a peak around midday and up to 30 % variation, recent intake of iron-containing food or supplements, and inflammation, which via hepcidin removes iron from the blood within hours ^{[2] [1]}.

Meaning arises only in the pattern with ferritin and transferrin saturation: low iron with low ferritin indicates absolute deficiency, low iron with normal or high ferritin indicates iron restriction due to inflammation. A persistently raised saturation (from 45 %) is the most sensitive first marker of haemochromatosis ^{[3] [1]}.

What moves this value?

Blood loss (menstruation, for example), little iron in the diet or coffee and tea with meals can lower absorption and the value.

Iron-rich food (meat, legumes, green vegetables) with a little vitamin C alongside supports absorption. Discuss a persistently low value with your doctor.

What this connects

• Ferritin

References

1. Pfeiffer, C. M. & Looker, A. C. Laboratory methodologies for indicators of iron status: strengths, limitations, and analytical challenges. Am J Clin Nutr 106, 1606S–1614S (2017). doi.org/10.3945/ajcn.117.155887
2. Bennett, C. et al. Serum iron and transferrin saturation variation are circadian regulated and linked to the harmonic circadian oscillations of erythropoiesis and hepatic Tfrc expression in mice. Am J Hematol 99, 2075–2083 (2024). doi.org/10.1002/ajh.27447
3. Olynyk, J. K. & Ramm, G. A. Hemochromatosis. N Engl J Med 387, 2159–2170 (2022). doi.org/10.1056/NEJMra2119758