Ironumol/L
Circulating iron (moment-in-time)
Also known as: Serum Iron
Typical optimal range
5.8–34.5 umol/L
A typical reference range is approximately 5.8–34.5 µmol/L, though exact ranges vary between laboratories, so always interpret your result against your own lab's reference interval. These figures are indicative — the range printed on your own lab report is the definitive one for your results.
Interpretation of iron studies in the UK generally follows NHS laboratory guidance and NICE clinical knowledge summaries on iron deficiency anaemia (NICE CKS: Anaemia — iron deficiency), which advise that ferritin is the preferred first-line test for assessing iron stores.
What is Iron?
Serum iron measures the amount of iron currently circulating in your bloodstream, bound to a transport protein called transferrin. Iron is essential for making haemoglobin — the protein in red blood cells that carries oxygen around the body — and also plays a role in energy production and immune function. Because serum iron fluctuates significantly throughout the day (and even hour to hour), it is considered a snapshot measurement and is generally most useful when interpreted alongside other iron markers such as ferritin, transferrin saturation, and TIBC (total iron-binding capacity).
What a high Iron means
A raised serum iron result is a prompt to look more closely at your iron status as a whole — it is not a diagnosis in itself, but it can point to a few different underlying situations worth discussing with your GP.
- Recent iron supplementation. Taking an iron supplement within 24 hours of a blood test is one of the most common reasons for a transiently high serum iron reading. This is a pre-analytical factor rather than a true clinical finding, which is why it is recommended to pause supplements before testing.
- Hereditary haemochromatosis. This relatively common genetic condition (particularly in people of Northern European ancestry) causes the body to absorb too much iron from food, leading to persistently elevated serum iron and transferrin saturation. The NHS offers testing and management pathways for haemochromatosis, and it is very treatable when caught early.
- Haemolysis. When red blood cells break down (haemolyse) — whether due to a medical condition or a handling issue with the blood sample itself — iron can be released into the serum, falsely elevating the result. Your GP or lab can identify whether sample haemolysis may have been a factor.
Serum iron alone is a poor diagnostic tool for iron overload; transferrin saturation and ferritin are more reliable. A single high reading — especially if you recently took a supplement or tested at the wrong time of day — often needs repeating under standardised conditions before any conclusions are drawn.
What a low Iron means
A low serum iron can suggest iron deficiency, but because the marker is so variable, ferritin is considered the more reliable first-line test for assessing iron stores — a low serum iron result should always be considered alongside ferritin and your full blood count.
- Iron deficiency. Insufficient dietary iron intake, poor absorption (for example in coeliac disease), or blood loss (including heavy periods) can all deplete iron stores and eventually lower circulating serum iron. Ferritin typically falls first, making it a more sensitive early marker of deficiency.
- Chronic disease or inflammation. Conditions that cause ongoing inflammation — such as chronic infections, autoimmune conditions, or kidney disease — can lower serum iron even when total body iron stores are adequate, as part of the body's acute-phase response. This is sometimes called anaemia of chronic disease.
A low serum iron result in isolation does not confirm iron deficiency anaemia; your GP will usually look at the broader picture including ferritin, haemoglobin, MCV, and symptoms before making any diagnosis or recommending treatment.
Should I be worried?
A single out-of-range serum iron result — high or low — rarely tells the full story on its own, and many everyday factors (the time of day you tested, a recent meal, or a supplement taken the previous day) can shift the number considerably. If your result falls outside range, it is worth mentioning to your GP, particularly if you have symptoms such as fatigue, breathlessness, or joint pain, or if other iron markers (ferritin, transferrin saturation) are also flagged. Your GP can arrange a repeat test under standardised conditions and look at the full iron panel alongside your full blood count to get a much clearer picture. There is no need to panic over a single reading, but it is a useful conversation starter.
What actually helps
Because serum iron is heavily influenced by when and how you test, as well as by diet and lifestyle, a few straightforward steps can make your results more accurate and meaningful.
- Test fasting, first thing in the morning. Serum iron follows a diurnal rhythm and is highest in the morning; testing fasted before 9 am gives the most consistent, comparable result over time. Eating before a test can also transiently raise serum iron.
- Pause iron supplements 24 hours before testing. Iron supplements can dramatically raise serum iron within hours of a dose, which can mask or exaggerate your true underlying status. Stopping supplementation for at least 24 hours before your blood draw gives a cleaner baseline reading.
- Maintain a balanced, iron-rich diet. For most people with adequate stores, a varied diet that includes both haem and non-haem iron sources supports healthy iron levels without the need for supplementation. If your GP has confirmed iron deficiency, they will advise on whether dietary changes or supplements are appropriate.
- Support iron absorption with vitamin C. Consuming vitamin C-rich foods alongside non-haem iron sources (plant-based iron) is well established to enhance absorption in the gut. Simple habits like squeezing lemon juice over lentils or having a glass of orange juice with a plant-based meal can make a practical difference.
There is good supporting evidence that the following foods help maintain healthy iron levels as part of a balanced diet.
Red meat (e.g. beef, lamb)
One of the richest sources of haem iron, which is absorbed more efficiently (around 20–30%) than non-haem iron from plant sources.
Liver and kidney
Organ meats are among the highest dietary sources of iron available; however, the NHS advises pregnant women to avoid liver due to its high vitamin A content.
Legumes (lentils, chickpeas, kidney beans)
Good plant-based sources of non-haem iron; pairing them with vitamin C helps offset the lower absorption rate compared to animal sources.
Dark leafy greens (spinach, kale)
Provide non-haem iron along with folate and other micronutrients that support red blood cell health, though absorption is partly limited by naturally occurring oxalates.
Fortified breakfast cereals
Many UK breakfast cereals are fortified with iron to levels that contribute meaningfully to daily intake, making them a practical option especially for those eating little or no meat.
Pumpkin seeds and other seeds
A convenient plant-based source of non-haem iron that also provides zinc and magnesium, contributing to broader nutritional balance.
Track your own Iron
Upload a lab PDF and Better Days trends Iron over time, flags it when it drifts, and suggests foods that help.
More in Vitamins/Minerals
Sources & further reading
These are reputable UK health resources for further reading. This page is written to be consistent with their guidance but is not a substitute for them.
For information only — not medical advice, and not individually reviewed by a clinician. Reference ranges vary by lab and individual. Discuss any results with a qualified clinician before making changes.