Iron, Total (Serum Iron) Test
The Iron, Total (serum iron) test measures the iron bound to transferrin in the circulation, reflecting iron in transit rather than total body stores. It has limited value in isolation owing to diurnal and day-to-day variability and sensitivity to recent intake, and is most informative within iron studies, where it combines with total iron-binding capacity to derive transferrin saturation.
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Biomarkers
Blood (serum)
Sample
1–3 business days
Turnaround
Yes — morning, fasting collection is preferred for reliability, with iron supplements withheld beforehand # REVIEWER FLAG: Confirm Access Medical Laboratories fasting and supplement-withholding guidance.
Fasting
What is the Serum Iron test?
The Iron, Total Test measures serum iron — the iron bound to transferrin in the circulation — providing one component of the assessment of iron status. It reflects iron in transit rather than total body stores, and is most informative when combined with total iron-binding capacity and ferritin within a full iron studies assessment. In the diagnostic landscape, serum iron alone has limited standalone utility because it varies through the day, fluctuates considerably between days, and rises after recent iron intake. Its value emerges in combination: paired with TIBC it yields transferrin saturation, which, with ferritin, distinguishes iron deficiency from iron overload and from the anaemia of chronic disease. Practitioners order serum iron as part of an iron panel, or where a specific component is needed, rather than as a substitute for ferritin, which remains the preferred single marker of iron stores. Standardised morning, fasting collection improves reliability.
What does the Serum Iron test measure?
Serum iron measures the quantity of iron bound to transferrin in the circulation, representing the iron in transit between absorption, storage, and utilisation rather than total body iron. Almost all circulating iron is transferrin-bound, with negligible free iron. The value shows marked diurnal variation, typically highest in the morning, and considerable day-to-day fluctuation, and rises transiently after dietary or supplemental iron intake.
Serum iron is of limited value in isolation because of its diurnal and day-to-day variability and its sensitivity to recent intake. It is clinically useful chiefly as a component of iron studies — combined with total iron-binding capacity (TIBC) to derive transferrin saturation — which together characterise iron deficiency and overload more reliably than serum iron alone. Ferritin remains the better marker of iron stores.
Why is the Serum Iron test ordered?
- Assessment of iron status as part of a full iron studies panel in suspected iron deficiency or overload
- Evaluation of microcytic anaemia alongside ferritin, TIBC, and transferrin saturation
- Investigation of suspected iron overload, such as hereditary haemochromatosis, where transferrin saturation derived from serum iron and TIBC is key
- Monitoring of iron status in patients on iron therapy, with appropriate attention to timing relative to dosing
- Assessment of iron status in chronic disease where the pattern across iron markers distinguishes deficiency from the anaemia of chronic disease
- Investigation of unexplained anaemia where a complete iron profile is required
- Evaluation where transferrin saturation specifically is needed to guide further investigation
Sample collection and turnaround
Sample type
Blood (serum)
Fasting required
Yes — morning, fasting collection is preferred for reliability, with iron supplements withheld beforehand # REVIEWER FLAG: Confirm Access Medical Laboratories fasting and supplement-withholding guidance.
Collection method
Venipuncture at patient service centre
Turnaround
1–3 business days
Collection notes
Collect in the morning after an overnight fast where possible, as serum iron is highest in the morning and rises after iron intake. Withhold iron supplements for an appropriate interval beforehand to reflect baseline status. Avoid haemolysis, which falsely raises the result. Best ordered as part of iron studies with TIBC and ferritin.
Specimen requirements
Minimum 0.5 mL serum. Separate serum from cells within 2 hours of collection; avoid haemolysed specimens.
What can affect Serum Iron results?
Serum iron is typically highest in the morning and falls later in the day, so morning collection is preferred and timing must be considered when interpreting or comparing results.
Iron from food or supplements raises serum iron transiently, so fasting collection and separation from recent iron dosing are advised to reflect baseline status.
Serum iron fluctuates substantially between days independent of true iron status, limiting the reliability of a single measurement and favouring interpretation within iron studies.
Acute-phase responses lower serum iron through hepcidin-mediated sequestration, contributing to the pattern of the anaemia of chronic disease independent of total body iron.
Haemolysis releases iron from red cells, falsely raising the measured serum iron, so haemolysed samples should be avoided.
Oestrogen-containing preparations can alter transferrin and iron measures, affecting serum iron and derived transferrin saturation. # REVIEWER FLAG: Confirm desired handling of this caveat.
What do Serum Iron results mean?
Elevated
A raised serum iron, particularly with a high transferrin saturation, suggests iron overload (such as haemochromatosis), recent iron intake, or release from tissue as in haemolysis or hepatic injury. It is interpreted with TIBC, transferrin saturation, and ferritin rather than alone, and a high transferrin saturation is a key trigger to investigate overload.
Normal
A normal serum iron does not exclude abnormal iron status given its variability and sensitivity to timing and intake. It is interpreted within the full iron studies pattern, and ferritin remains the better guide to body iron stores.
Reduced
A low serum iron occurs in iron deficiency but also in the anaemia of chronic disease, where inflammation lowers circulating iron despite adequate or increased stores. The accompanying TIBC and ferritin distinguish these: high TIBC with low ferritin favours deficiency, whereas low or normal TIBC with normal or raised ferritin favours chronic disease.
Note: Serum iron is unreliable in isolation owing to diurnal variation, day-to-day fluctuation, and sensitivity to recent intake, and should be interpreted as part of iron studies with TIBC, transferrin saturation, and ferritin. Morning, fasting collection improves reliability, and haemolysis falsely raises the result. Ferritin, not serum iron, is the preferred single marker of iron stores.
Frequently asked questions
It measures the iron bound to transferrin in the circulation, representing iron in transit rather than total body stores. It is most informative as part of iron studies with TIBC and ferritin.
How to access the Serum Iron test
The Serum Iron reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: June 3, 2026
Last reviewed: June 3, 2026
- Camaschella C. Iron-deficiency anemia. N Engl J Med. (2015)
- Pasricha SR, et al. Iron deficiency. Lancet. (2021)
- Wish JB. Assessing iron status: beyond serum ferritin and transferrin saturation. Clin J Am Soc Nephrol. (2006)
- Kowdley KV, et al. ACG Clinical Guideline: Hereditary Hemochromatosis. Am J Gastroenterol. (2019)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.
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