Serum Iron
Fe· also: Serum Iron, Iron
Clinical Overview
Serum iron measures the amount of iron circulating in the bloodstream bound to transferrin. It fluctuates significantly throughout the day (diurnal variation) and is affected by recent iron intake, making it less reliable as a standalone test. Serum iron is most useful when interpreted alongside TIBC and ferritin to assess iron status comprehensively.
Why This Test Matters
Serum iron alone is insufficient to diagnose iron deficiency or iron overload. The transferrin saturation (serum iron ÷ TIBC × 100%) is a more useful derived value: low saturation (<20%) confirms iron-deficient erythropoiesis; high saturation (>45–50%) suggests iron overload and triggers testing for hemochromatosis (HFE gene mutations). Serum iron is diurnal — morning values are up to 30% higher than afternoon values.
Reference RangesWHO/IFCC standards
| Age Group | Sex | Reference Range | Unit | Notes |
|---|---|---|---|---|
| Adults (18–64) | Male | 65 – 175 | µg/dL | — |
| Adults (18–64) | Female | 50 – 170 | µg/dL | — |
Also reported in: µmol/L.
What Causes Abnormal Results?
High Fe Causes
- Hemochromatosis (hereditary iron overload)
- Iron overload from multiple blood transfusions
- Liver disease (iron released from damaged cells)
- Iron supplementation or infusion
- Hemolysis (iron released from red cells)
Low Fe Causes
- Iron deficiency anemia
- Anemia of chronic disease / inflammation
- Chronic blood loss
Signs & Symptoms to Watch For
How to Prepare for This Test
Draw in the morning (7–10 AM) after fasting for 12 hours — serum iron has a strong diurnal variation and rises after meals. Avoid iron supplements for 24 hours before testing.
Factors That Can Affect Results
- Time of day (morning values are 20–30% higher than afternoon — standardize timing)
- Recent dietary iron intake (raises serum iron transiently)
- Inflammation and infection (acute phase reaction lowers serum iron)
- Recent blood transfusion (raises serum iron)
Related Topics
Frequently Asked Questions
What is transferrin saturation and why is it important?
Transferrin saturation = (serum iron ÷ TIBC) × 100%. It measures what percentage of transferrin is actually loaded with iron. Normal is 20–45%. Below 20%: iron-deficient erythropoiesis (iron supply is insufficient for red cell production). Above 45–50%: iron overload, triggering HFE gene testing for hereditary hemochromatosis. It is more clinically useful than serum iron alone because it is less affected by inflammation.