Serum Iron
Serum Iron
What this test measures
Serum iron measures the amount of iron circulating in your blood. Iron is essential for making haemoglobin, which carries oxygen in your red blood cells. This test is often done alongside ferritin and other iron tests to get a full picture of your iron levels.
Understanding the numbers
Typical range: 10-30 µmol/L
Levels vary throughout the day, usually higher in the morning. Results are best interpreted alongside ferritin and transferrin saturation.
- Low: 0–10 µmol/L
- Normal: 10–30 µmol/L
- Raised: 30–50 µmol/L
Key numbers
- 10 µmol/L — Lower limit — low suggests iron deficiency
- 30 µmol/L — Upper limit — high suggests iron overload
Typical UK laboratory range. Serum iron swings widely throughout the day and between meals — it is never used alone. Always interpret with ferritin and transferrin saturation to distinguish iron deficiency, anaemia of chronic disease, and iron overload.
Ranges can vary slightly between laboratories — your report may show slightly different numbers. This page does not read or interpret your result; your GP looks at it alongside your history and other tests.
What a higher-than-normal result can mean
- You may have too much iron in your blood
- Can be caused by taking iron supplements
- May suggest a condition called haemochromatosis (iron overload)
- Liver problems can also cause high serum iron
- Your GP may do more tests to find the cause
Questions you could ask your GP
- Should I have my ferritin and transferrin checked as well for a complete picture?
- What might be causing my iron levels to be abnormal?
- Do I need to change my diet or take supplements?
- Could there be an underlying condition affecting my iron absorption?
Example stories
These are made-up examples to show how results are talked about in real appointments. They are not real patients.
Low serum iron, heavy periods
Keisha's serum iron was 6 µmol/L, ferritin 8 µg/L and transferrin saturation 8%. Haemoglobin 108.
What the GP said: “The three iron tests agree: this is iron deficiency. Iron tablets and we'll treat the heavy periods. The ferritin is the most reliable of the three numbers, but they all tell the same story today.”
What happened next: After six months of iron and tranexamic acid for periods, iron studies normalised.
When the three iron measures (ferritin, serum iron, transferrin saturation) all point the same way, the diagnosis is straightforward. When they disagree, it usually means inflammation is confusing the picture.
High serum iron — haemochromatosis
Omar's iron studies showed serum iron 42, ferritin 950, transferrin saturation 72%. His father had haemochromatosis.
What the GP said: “This is the classic pattern of hereditary haemochromatosis. I'll arrange HFE genetic testing and refer you for venesection planning.”
What happened next: HFE was positive. Omar started venesection and his iron stores came down over 18 months.
A persistently high serum iron with high ferritin and high transferrin saturation strongly suggests haemochromatosis — especially with a family history. Early treatment prevents damage to the liver, heart and joints.
'Normal' serum iron but really iron-deficient
Lila had a chronic infection. Her serum iron was 14 (within range) but her ferritin was 180 (raised — due to inflammation) and her transferrin saturation was 12%.
What the GP said: “Chronic infection raises ferritin and can hide true iron deficiency. The low transferrin saturation tells us you actually do have functional iron deficiency. Treating the infection is the first step; we may need intravenous iron if you don't recover.”
What happened next: After the infection cleared and IV iron, her iron studies normalised and her haemoglobin recovered.
A 'normal' serum iron in someone with inflammation can still be iron-deficient. The transferrin saturation often cuts through the confusion — a low saturation with a high ferritin means functional iron deficiency.
Spuriously high after iron tablets
Aditya had been taking iron tablets for a month for previous iron deficiency. He had taken his morning dose two hours before the blood test. His serum iron was 36 µmol/L.
What the GP said: “Serum iron goes up sharply after iron tablets. To get a true baseline we need to repeat the test in the morning, fasting, having skipped iron for at least 24 hours.”
What happened next: A repeat fasting iron 24 hours off iron tablets was 18 µmol/L — normal.
Serum iron is easily misleading because it rises after meals and iron tablets. Always check the test was done in the morning, fasting, before drawing conclusions from a single value.
Before you act on anything here
This page is general information, written to help you understand — it is not personal medical advice and it cannot tell you what is right for you. Talk to your own GP, pharmacist or nurse about your own health.
- Need help now but it's not an emergency? Call NHS 111 or use 111.nhs.uk.
- Emergency? Call 999 or go to A&E.