Serum Iron

Serum iron measures the amount of iron actually circulating in your blood at the moment of the draw, most of it bound to the transport protein transferrin. It's a single-moment snapshot rather than a measure of your reserves, so it can look normal even when stored iron is low. That's why it's interpreted alongside ferritin, TIBC, and transferrin saturation rather than on its own.

A typical adult male reference range is roughly 65–175 µg/dL, with some variation by lab. Because serum iron swings widely through the day and with recent meals or supplements, the single number matters less than how it fits with the rest of the iron panel. Compare against your own lab's range and look at the full picture.

Serum iron follows a pronounced daily (diurnal) rhythm, often peaking in the morning and dropping later in the day, and it also rises after iron-containing meals or supplements. Swings of a large percentage within a single day are normal. This variability is exactly why ferritin and transferrin saturation are considered more reliable indicators of iron status than a lone serum iron value.

Many clinicians prefer a morning, fasting draw for serum iron to reduce the noise from diurnal variation and from recent food or supplements. Iron pills in particular can transiently spike the result, so labs often ask you to hold supplements beforehand. Follow your provider's specific instructions, and try to test under the same conditions each time so your trend is comparable.

Serum iron is the numerator in the transferrin saturation calculation: TSAT is serum iron divided by TIBC, the total capacity of transferrin to carry iron. On its own serum iron is hard to interpret, but paired with TIBC it tells you how full your transport system is. Reading iron, TIBC, TSAT, and ferritin together is what separates iron deficiency from iron overload.