Serum Iron
Also written as: Iron, Fe
The amount of iron circulating in the blood at the moment of the draw, which varies through the day.
What it measures
The concentration of iron travelling in the blood, where it is carried by a protein called transferrin. It reflects iron in transit at that moment, not the body's total iron stores.
Why a doctor orders it
Usually ordered as part of an iron panel alongside TIBC and ferritin when anemia, fatigue, or iron overload is being investigated. On its own it is hard to interpret, because the level swings widely from hour to hour and day to day.
What is generally associated with a higher result
Broadly associated with iron overload conditions, recent iron supplementation, liver conditions, and some anemias in which the body cannot use iron properly. A recent iron tablet or iron-rich meal can raise it for several hours.
What is generally associated with a lower result
Broadly associated with iron deficiency, but also with recent illness or inflammation, which temporarily pulls iron out of the bloodstream. A single low value does not by itself establish depleted iron stores.
Everyday things that move this number
Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:
- Time of day - iron is typically higher in the morning
- Iron supplements or multivitamins taken in the days before the draw
- A recent iron-rich meal
- Any recent illness, infection, or inflammation
- The menstrual cycle
Questions to take to your appointment
- Was this taken as part of a full iron panel with ferritin and TIBC?
- Should a repeat sample be done fasting and in the morning?
- Could a recent illness have temporarily shifted this value?
Build a printable questionnaire with your own results →
Where to read more
MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .
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