When this test may help
Brain fog alone is too broad. What suggests low iron?
Ferritin may help if you feel tired, exercise feels harder, or your legs feel restless. Heavy periods, pregnancy, recent bleeding, or poor iron absorption also raise the chance of low iron. Stored iron can be low even when a complete blood count, or CBC, looks normal.
Loss
You may lose iron faster than you replace it
Heavy menstrual bleeding, gut or urinary blood loss, surgery, childbirth, and regular blood donation can cause iron loss.
Need
The body may need more than usual
Pregnancy and growth change iron needs. Age and pregnancy change what the result means and its likely cause.
Absorption
You may not take in iron well
Inflammatory bowel disease, coeliac disease, gastrointestinal surgery, and a restricted diet can change the workup.
Ferritin can show low iron stores. It can't show where the iron went. Blood loss, higher need, lower intake, and poor absorption call for different plans.
Age and sex
Age, sex, periods, pregnancy, and illness change what ferritin results mean.
The lab may use age and sex to set its range. Tell the clinician about periods, pregnancy, menopause, and any illness that can raise ferritin.
Children and teenagers
Children need a range for their age. Fast growth raises iron needs, and periods add regular iron loss. A recent infection can raise ferritin and hide low iron stores.
People who menstruate
Heavy periods are a common cause of low iron stores before menopause. Record how much you bleed and for how long.
Pregnancy and after birth
Iron needs rise during pregnancy and ferritin changes as pregnancy progresses. Tell your doctor if you're pregnant or recently gave birth. Be sure to mention any bleeding so the result is read at the right stage of care.
Men and people after menopause
Low iron stores without a clear reason need more checks. A clinician may look for bleeding from the gut or urinary tract and for coeliac disease instead of assuming diet is the cause.
Older adults and chronic illness
Ferritin can be harder to interpret in older adults because inflammation and other illnesses may raise it. A result that looks reassuring on the report may still need the CBC, symptoms, and wider health context.
Before the appointment
Ask about preparation. Bring medicine and supplement labels and older results.
Ask how to prepare. You may need to fast for 12 hours or give a morning sample when you're also having other iron tests.
Bring photos of medicine and supplement labels. Also bring older ferritin, CBC, or iron-test results with their dates.
Mention a recent illness, pregnancy or birth, heavy periods, blood donation, or other bleeding. These details change what the result means.
The blood draw
A health professional takes a small sample from a vein in your arm. The collection usually takes less than five minutes. You may feel a brief sting.
After the blood draw
Brief soreness or a small bruise can happen where the needle went in. These usually settle quickly.
What the result can mean
Ferritin has no universal target for brain fog.
Start with the range on your report, then add your age, sex, pregnancy status, symptoms, CBC, and any inflammation.
If the result is low
Lower than expected for the clinical context
Low ferritin supports low iron stores. The clinician should look for the cause, such as bleeding, pregnancy, low iron intake, or poor absorption.
If the result is in range
Inside your lab's range
Low iron stores are less likely in a healthy adult. Inflammation or a long-term illness can raise ferritin and hide low iron stores.
If the result is high
Higher than your lab's range
High ferritin can come from inflammation, infection, liver or kidney disease, metabolic illness, cancer, or too much iron. Other tests must tell these causes apart.
What can hide low iron
Inflammation can push ferritin up.
A result inside or above the lab's range doesn't rule out iron deficiency. That's why the clinician may compare ferritin with symptoms, the CBC, transferrin saturation, CRP, illness history, and liver or kidney health.
Why the cutoffs look inconsistent
Each row is for a different situation. They aren't competing “optimal” targets.
This guideline counts below 15 µg/L as iron deficiency and 15 to 30 µg/L as probable. It says there's no sharp line, so values still need clinical judgment.
The American Gastroenterological Association recommends a ferritin cutoff of 45 ng/mL, not 15 ng/mL, to diagnose iron deficiency in people with anemia.
Below 70 µg/L may indicate iron deficiency. WHO labels this a conditional recommendation based on low-certainty evidence and advises accounting for inflammation.
Reference ranges depend on age, sex, and laboratory method. Inflammation or liver-cell damage can make a result within the range harder to interpret.
What you can do
Use food to support iron intake while you work out the cause.
Iron-rich foods can support your intake while you check why your ferritin is low.
Choose iron-rich foods you already eat
Options include lean meat, seafood, poultry, iron-fortified cereals and breads, beans, lentils, peas, spinach, nuts, and dried fruit. Pick the foods that fit your diet, budget, culture, and stomach.
Pair plant iron with vitamin C
Have beans, lentils, greens, or fortified cereal with foods such as citrus fruit, strawberries, peppers, tomatoes, or broccoli. Vitamin C helps your body absorb the iron in plant foods.
Get enough iron on a plant-based diet
Well-planned vegetarian or vegan diets can provide enough iron, but the body absorbs plant iron less easily. If a restricted diet or gut symptoms make meals difficult, a registered dietitian can help you build a workable food plan.
Food can improve iron intake. It can't stop ongoing blood loss or correct an absorption problem. High doses of iron can cause harm, and iron supplements are dangerous to children. Treatment should be based on the result, the cause, and a plan you understand.
Use the result
Keep the exact result for your next visit.
Keep these together
- Ferritin value and unit
- The lab's reference range
- Collection date and whether you were ill then
- CBC and other iron-test results collected at the same time
Question for the visit
“What could explain this ferritin result, and do the CBC, transferrin saturation, symptoms, or inflammation change how you read it?”
Save this check
Keep this guide in My Fog.
Saving adds ferritin to Saved Checks, so you can find this guide again when the result arrives or before an appointment.
My Fog saves the check, not the laboratory report. Keep the original report in your health record.
Common questions about Ferritin
Ferritin blood test levels: what is a normal range?
MedlinePlus lists a normal ferritin range of 30 to 400 ng/mL for males and 13 to 150 ng/mL for females. Labs differ slightly, so use the range printed on your own report. MedlinePlus adds that the lower your number is, even inside the normal range, the more likely your iron stores are low.
Source: MedlinePlus
Can low ferritin cause brain fog?
Too little iron can lead to iron-deficiency anemia. This can cause tiredness, shortness of breath, and trouble with memory and concentration, MedlinePlus says. In a 2007 trial of 149 women aged 18 to 35, women with enough iron did thinking tasks better and faster than women with iron deficiency anemia. Women with low iron but no anemia scored in between.
Sources: MedlinePlus, Murray-Kolb 2007
Ferritin supplement: does taking iron help with tiredness?
Iron supplements are the usual treatment for low iron, MedlinePlus says. In a 2012 trial of 198 tired women with ferritin below 50 µg/L and no anemia, 12 weeks of iron supplements cut fatigue scores by 47.7%, against 28.8% with placebo. The NHS lists constipation, diarrhea, tummy pain, heartburn and feeling sick as side effects.
Sources: MedlinePlus, Vaucher 2012, NHS
How long does it take to raise ferritin?
Blood counts return to normal after 2 months of iron supplements for most people, MedlinePlus says. It says to keep taking them for another 6 to 12 months to build up iron stores. In a 2012 trial of women with ferritin below 50 µg/L, 12 weeks of iron raised ferritin 11.4 µg/L more than placebo.
Sources: MedlinePlus, Vaucher 2012
How accurate is a ferritin blood test?
A 2021 Cochrane review pooled nine studies of 512 adults seeking medical care. With a cutoff of 30 µg/L, ferritin found 79% of the people with iron deficiency. It correctly cleared 98% of the people without it. So about one in five people with iron deficiency scored 30 µg/L or higher. The review rated this evidence as low certainty.
Source: Garcia-Casal 2021
Ferritin blood test at home: are finger-prick kits accurate?
Ferritin in a finger-prick sample can change before the lab tests it. In a 2023 study, it changed more than the study allowed after 24 hours at room temperature. A 2024 study of 46 volunteers tested a home finger-prick tube after 120 hours. Ferritin met two of three acceptance criteria. The authors did not call it suitable for ferritin.
Sources: Maroto-García 2023, Kurstjens 2024
Ferritin blood test name: what the lab order may say
The order or report may say serum ferritin, serum ferritin level or ferritin serum. All three names mean the same blood test. Ferritin is one of several iron tests. MedlinePlus lists three others: serum iron, transferrin and total iron-binding capacity (TIBC). Ferritin is the one that measures how much iron your body has stored.
Sources: MedlinePlus, MedlinePlus
Evidence
Sources for Ferritin
What the test measures, the blood draw, preparation, and basic result limits
Iron stores, inflammation, deficiency, and overload cutoffs
Primary-care indications, the ferritin continuum, CBC context, and finding the cause
Why a high ferritin result doesn't diagnose iron overload
The ferritin cutoff used when anemia is already present
Specimen, laboratory method, reference intervals, and inflammatory limits
Age and sex differences, iron-rich foods, plant iron absorption, and supplement safety
See each claim's source
indication
Ferritin is an iron-storage protein, and serum ferritin is used to assess iron stores.procedure
Ferritin is measured from a venous blood sample, and the collection itself usually takes less than five minutes.preparation
A clinician may request a 12-hour fast and morning collection, so patients should follow the instructions on the order rather than assume there is no preparation.interpretation
Ferritin values lie on a continuum, and cutoffs need clinical interpretation based on the patient and setting.range
Ferritin cutoffs differ across otherwise well adults, patients with anemia, and people with inflammation, so one universal optimal range is not medically defensible.limitation
Inflammation can raise ferritin and make an apparently normal or high result unreliable as a standalone measure of iron stores.safety
A high ferritin result does not diagnose iron overload and should be evaluated with clinical history and other laboratory findings.context
Ferritin interpretation changes with age, sex, menstrual blood loss, pregnancy, older age, and the presence of inflammation or chronic illness.diet
Iron-rich foods can support iron intake, and vitamin C improves absorption of nonheme iron from plant foods.safety
High-dose iron supplements can cause harm, and iron-containing products can cause fatal poisoning in young children.