Iron
Also known as: Serum Iron, Fe
What Does Iron Measure?
Serum iron measures the amount of circulating iron bound to a protein called transferrin in your bloodstream. Unlike the iron stored in your body's tissues and organs, this test specifically captures the iron actively being transported through the blood at the time of the draw. The result reflects a snapshot of your iron availability for red blood cell production and other critical metabolic functions.
Why Does Iron Matter?
Iron is essential for producing hemoglobin, the protein inside red blood cells that carries oxygen from your lungs to every cell in your body. Without adequate iron, your body cannot manufacture enough healthy red blood cells, leading to iron-deficiency anemia, fatigue, impaired cognitive function, and weakened immunity. Conversely, too much iron in the blood can be toxic, damaging organs like the liver, heart, and pancreas over time. Serum iron is rarely interpreted alone — it is most meaningful when evaluated alongside ferritin, transferrin saturation, and TIBC to paint a complete picture of your body's iron status and storage.
Normal Ranges
Males
60–170 mcg/dL (10.7–30.4 µmol/L)
Females
50–170 mcg/dL (9.0–30.4 µmol/L)
Children
50–120 mcg/dL (varies by age; infants may have higher levels)
Causes of High Levels
- Hereditary hemochromatosis — a genetic disorder causing excessive iron absorption from food
- Iron supplementation overdose or excess intake of iron-containing supplements
- Frequent blood transfusions leading to iron accumulation in tissues
- Hemolytic anemia — destruction of red blood cells releases stored iron into circulation
- Liver disease (hepatitis or cirrhosis) causing iron to leak from damaged liver cells
- Lead poisoning or certain toxic exposures that interfere with iron metabolism
Causes of Low Levels
- Iron-deficiency anemia — the most common cause, often due to inadequate dietary intake
- Chronic blood loss from heavy menstrual periods, gastrointestinal bleeding, or ulcers
- Poor dietary intake of iron-rich foods, especially in vegetarians and vegans
How to Improve Your Iron
Diet
- Eat heme iron-rich foods such as red meat, poultry, and fish, which are absorbed 2–3 times more efficiently than plant-based iron
- Incorporate plant-based (non-heme) iron sources like lentils, chickpeas, tofu, spinach, and fortified cereals
- Pair iron-rich foods with vitamin C sources (bell peppers, citrus, strawberries) to enhance non-heme iron absorption by up to 3-fold
- Avoid drinking coffee, tea, or consuming calcium-rich foods within 1–2 hours of iron-rich meals, as these inhibit iron absorption
- Cook in cast iron cookware, which can transfer small but meaningful amounts of dietary iron into food
Supplements
- Ferrous sulfate 325 mg (65 mg elemental iron) taken every other day has shown comparable absorption with fewer gastrointestinal side effects than daily dosing
- Ferrous gluconate 300 mg (36 mg elemental iron) is a gentler alternative for those sensitive to ferrous sulfate
- Iron bisglycinate (chelated iron) 25–36 mg daily is well tolerated and highly bioavailable with minimal constipation
- Vitamin C (250–500 mg) taken alongside iron supplements significantly boosts absorption
Related Biomarkers
Frequently Asked Questions
What is the difference between serum iron and ferritin?
Serum iron measures the iron actively circulating in your bloodstream at a single moment in time, while ferritin reflects your body's long-term iron storage. Ferritin is generally considered a more reliable indicator of true iron deficiency or overload because it is less affected by recent meals or short-term fluctuations. Doctors typically look at both together — low serum iron with low ferritin strongly suggests iron deficiency, while low serum iron with normal or high ferritin may point to chronic inflammation.
Can serum iron levels change throughout the day?
Yes, serum iron levels show significant diurnal (daily) variation — they tend to be highest in the morning and can drop by as much as 30–40% by late afternoon or evening. This is why blood draws for serum iron are typically recommended in the morning after an overnight fast to ensure consistent and accurate results. Eating before the test can also temporarily raise serum iron levels.
What symptoms might suggest my iron is too low?
Common symptoms of low iron include persistent fatigue and low energy, paleness of the skin or inner eyelids, shortness of breath with light activity, cold hands and feet, brittle nails, hair thinning or loss, frequent headaches, difficulty concentrating (brain fog), and an unusual craving to eat non-food items like ice or dirt (called pica). These symptoms often develop gradually and can be mistaken for general stress or poor sleep.
Is it possible to have normal serum iron but still be iron deficient?
Yes, absolutely. In the early stages of iron deficiency, your body first depletes its iron stores (reflected by a dropping ferritin level) before serum iron falls. This stage is called 'iron depletion' — ferritin may be very low while serum iron remains temporarily normal. This is why ferritin is often considered the most sensitive early marker of iron deficiency, and why doctors evaluate multiple markers together rather than relying on serum iron alone.