Iron, Serum
The amount of iron travelling in your blood at the moment of the draw. It swings with meals, supplements and the time of day.
AI-verified against cited sources. Awaiting expert reviewAlso called FeLOINC 2498-4
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The usual range for Iron depends on sex. Choose female or male above to see where you stand.
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What it is
Serum iron measures the iron carried in your blood, attached to a protein called transferrin. It is usually reported with TIBC, transferrin saturation and ferritin. Unlike ferritin, which reflects the iron you have in storage, serum iron is a snapshot. It can change within hours after an iron pill or an iron-rich meal, and it varies through the day.
Why it matters
Your body needs iron to make hemoglobin, the protein in red blood cells that carries oxygen. Serum iron helps your clinician work out whether low hemoglobin or small red cells are caused by low iron, inflammation or something else. On its own it isn't very reliable, so it is read together with TIBC, transferrin saturation and ferritin.
If it’s low
A low serum iron fits with low iron stores. But it also drops during inflammation or infection even when stores are fine, which is why it is read together with ferritin and TIBC.
Common causes
- Not enough iron in the diet
- Heavy periods or other blood loss
- Pregnancy
- Poor iron absorption in the gut
- Inflammation, infection or other long-term illness, which can lock iron away in storage
- Slow bleeding in the stomach or bowel
What can help
- Ask your clinician to look at ferritin, TIBC and transferrin saturation together
- Ask what may be behind a low level and whether iron treatment is right for you
- Eat iron-rich foods such as meat, fish, beans, lentils and iron-fortified cereals
If it’s high
A high serum iron is often temporary, for example after iron pills taken shortly before the test. Less often it can be a sign of iron overload, liver cell injury, or red blood cells breaking down faster than normal.
Common causes
- Iron pills or a multivitamin with iron taken shortly before the blood draw
- A recent iron-rich meal
- Recent blood transfusions or iron injections
- Liver inflammation, such as hepatitis
- Hemolytic anemia, where red blood cells break down early
- Iron overload conditions, including the inherited condition hemochromatosis
- Iron poisoning from swallowing iron pills, which is an emergency
What can help
- Tell your clinician if you took iron or ate an iron-rich meal before the sample, since a repeat fasting morning draw may be suggested
- Ask whether ferritin, TIBC and transferrin saturation should be read together with it
- Keep iron-containing supplements where children can't reach them
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
The usual range depends on sex and age. Choose women or men to see the one that applies.
- Men, 18+38–169 µg/dL
Sources: Labcorp, ARUP Laboratories, MedlinePlus Medical Encyclopedia (NIH)
- Women, 18–5927–159 µg/dL
Sources: Labcorp, ARUP Laboratories, MedlinePlus Medical Encyclopedia (NIH)
- Women, 60+27–139 µg/dL
Source: Labcorp
See Iron by age and sex, with the U.S. survey numbers where they exist.
If this applies to you
Iron means a little more for some people. Open the one that fits you.
Low iron or anemia
Serum iron is part of the usual iron studies, along with TIBC and transferrin saturation. BSG lists a low serum iron among the signs of iron deficiency, but ferritin is the more useful single test.
How common is your level?
NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.
Use the left and right arrow keys to read each age. Shift moves five years.
Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2015-2016, 2017-March 2020 (pre-pandemic), August 2021-August 2023. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.
Explore Iron by age and sex: every percentile as a table, with a download.
What can affect your result
- Time of day: serum iron varies through the day, so labs usually ask for a morning sample
- Recent iron pills, multivitamins with iron or an iron-rich meal
- Infection and inflammation, which lower serum iron
- Sex, age and menstrual blood loss
- Pregnancy
- Medicines, including birth control pills and estrogens, testosterone and some antibiotics
- A recent blood transfusion or iron injection (Labcorp advises waiting at least four days after a transfusion)
- A hemolyzed sample or an EDTA tube, which can give a wrong result
- Iron pills, multivitamins with iron or an iron-rich meal shortly before the draw can raise the result. MedlinePlus says the level depends on how recently iron was taken in.
- Labcorp asks that the sample be drawn before iron treatment is given, and that iron testing wait at least four days after a blood transfusion.
- Infection and inflammation lower serum iron even when iron stores are fine.
- Gross hemolysis can interfere, and EDTA plasma gives falsely low results. Labs need serum or lithium heparin plasma.
- Medicines listed by MedlinePlus as able to change the result include birth control pills and estrogens, testosterone, some antibiotics, blood pressure and cholesterol medicines, gout medicines and deferoxamine.
Morning. Serum iron varies through the day, so labs usually ask for a morning sample. Changes within hours of iron intake, so it reflects the last day or so and not long-term iron stores.
When to talk to a clinician
If you or a child may have swallowed iron pills, call your local emergency number or poison control right away. Some labs, such as ARUP, treat a serum iron above 500 µg/dL (about 90 µmol/L) as needing prompt attention. Talk with a clinician soon if your iron is low and you have tiredness, shortness of breath, dizziness, or black, tarry or bloody stools.
Questions you could ask
- Is serum iron worth tracking over time, or is ferritin more useful for me?
- Could a supplement, a meal or the time of day have affected this result?
- Should we repeat it on a fasting morning sample?
- Should we look at transferrin saturation and ferritin together?
- Could inflammation or a recent illness explain a low iron level?
- Should we check ferritin, TIBC and transferrin saturation as well?
Questions people ask
Do I need to fast before a serum iron test?
Usually a morning draw, and often a fast. MedlinePlus says serum iron is likely to be drawn in the morning or after fasting, because the level changes with how recently you took in iron. Follow the instructions from your lab or clinician.
Why is my serum iron low when my ferritin is normal?
Serum iron is a snapshot. It drops with infection or inflammation and varies through the day, while ferritin reflects your stored iron. A low iron with a normal ferritin can be a short-lived dip. Your clinician can use TIBC and transferrin saturation to put it in context.
Do iron pills change the result?
Yes. Serum iron can rise within hours of an iron pill or an iron-rich meal, which can make the result look higher than your usual level. Labcorp asks that the sample be drawn before iron treatment is given. Ask your clinician or the lab how to time your pills around a blood draw.
How do I convert µg/dL to µmol/L?
Multiply µg/dL by 0.179 to get µmol/L. To go the other way, multiply µmol/L by 5.585. For example, 100 µg/dL is about 17.9 µmol/L.
Why is the range on my report different from one I saw online?
Labs use different methods and reference groups. For adult men, Labcorp lists 38–169 µg/dL, ARUP lists 45–182 µg/dL and MedlinePlus lists 59–158 µg/dL. Use the range printed on your own report.
Show the science and sources
Units
- 1 µg/dL = 1 µg/dL
- 1 µg/dL = 0.1791 µmol/L
Is a change real?
Iron naturally varies about 28% from test to test in the same healthy person. Between two results from the same lab, a rise of 115% or more, or a fall of 53% or more, is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Biological variation of serum iron from the European biological variation study (EuBIVAS) (Carobene A et al.).
For clinicians and researchers
Serum iron is transferrin-bound iron, measured by colorimetric or spectrophotometric methods (Labcorp, ARUP). It has a marked diurnal pattern and responds within hours to oral iron, so it is a poor stand-alone marker of iron status, and Labcorp notes that ferritin is more sensitive for both deficiency and overload. Serum iron has long been described as varying through the day, and a 2024 mouse study found it follows an endogenous circadian rhythm. Inflammation lowers serum iron through hepcidin-driven iron sequestration, so low iron with high ferritin and low TIBC points toward inflammation rather than iron deficiency. Labcorp's pre-analytical notes: use serum or lithium heparin plasma (EDTA lowers results), separate cells within 45 minutes, avoid gross hemolysis, draw before iron therapy, and wait at least four days after a transfusion. Reference intervals vary by lab: adult men 38–169 µg/dL at Labcorp and 45–182 µg/dL at ARUP; adult women 27–159 µg/dL at Labcorp (to age 60) and 28–170 µg/dL at ARUP. The SI factor is 1 µmol/L = 5.585 µg/dL. ARUP's critical-value list flags serum iron above 500 µg/dL.
LOINC 2498-4 (primary), 14798-3, 35214-6. Specimen: serum-or-plasma.
Sources
- Iron (test 001339), Labcorp
- Iron and Total Iron-binding Capacity (TIBC) (test 001321), Labcorp
- Pediatric Testing Reference Ranges, Labcorp (2022)
- Iron, Plasma or Serum (test 0020037), ARUP Laboratories
- Critical Values List, ARUP Laboratories
- Serum iron test, MedlinePlus Medical Encyclopedia (NIH)
- Iron (compound summary, CID 23925), PubChem (NIH)
- Serum iron and transferrin saturation variation are circadian regulated and linked to the harmonic circadian oscillations of erythropoiesis and hepatic Tfrc expression in mice, American Journal of Hematology (2024)
- SI Conversion Calculator (AMA Manual of Style), American Medical Association / Oxford University Press
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.