Units: ng/mL (or µg/L — equivalent) · Functional optimal: 50-150 ng/mL (functional optimal for energy in adults) · Clinical reference: Women 15-200 ng/mL · Men 30-400 ng/mL (lab reference)
Ferritin reflects your body's iron stores. Low ferritin is one of the most common drivers of unexplained fatigue; very high ferritin can flag inflammation or iron overload.
Ferritin is the body's main iron-storage protein. Serum ferritin levels correlate with total body iron stores in the absence of inflammation. It is the best single test for diagnosing iron deficiency.
Why it matters
Iron deficiency — even before anemia develops — causes fatigue, hair loss, exercise intolerance, restless legs, and cognitive sluggishness. On the other end, persistently elevated ferritin can flag inflammation, fatty liver, or hereditary hemochromatosis (HFE variants).
Causes of high & low levels
Causes of high Ferritin
Inflammation (ferritin is an acute-phase reactant) — pair with CRP
Inadequate dietary iron, plant-based diets without planning
Heavy menstrual bleeding
Gastrointestinal blood loss (ulcers, colon cancer screening matters)
Pregnancy — increased demand
Malabsorption (celiac disease, H. pylori, after bariatric surgery)
Endurance athletes — high turnover plus footstrike hemolysis
Lifestyle
Investigate heavy menstrual bleeding or GI symptoms early
Donate blood if ferritin runs very high in healthy adults — under medical guidance
Nutrition
Heme iron sources (red meat, poultry, fish) absorb best
Pair plant iron (lentils, spinach, tofu) with vitamin C to boost absorption
Coffee and tea reduce non-heme iron absorption — separate by 1-2 hours from iron-rich meals or supplements
For supplements, ferrous bisglycinate is well tolerated; take every other day for better absorption
Testing notes
Always interpret ferritin alongside hemoglobin, transferrin saturation, and CRP. Inflammation can artificially raise ferritin and mask true deficiency.
Related in the knowledge graph
Symptoms
Fatigue — Iron deficiency (ferritin < 50) is one of the most common reversible causes of chronic fatigue. Strong evidence
Frequently asked questions about Ferritin
What ferritin level causes fatigue?
Many people feel symptoms — fatigue, hair shedding, exercise intolerance — when ferritin drops below 50 ng/mL, even though most labs only flag deficiency under 15-30 ng/mL. Restoring ferritin into the 50-100 range often resolves symptoms.
Should I take iron if my ferritin is low?
Talk to a clinician first. Replacing iron is usually appropriate, but the underlying cause (heavy periods, GI bleeding, malabsorption) needs investigation — otherwise it will recur.
What if my ferritin is very high?
Persistently elevated ferritin warrants checking transferrin saturation and inflammatory markers. If transferrin saturation is also high, HFE genetic testing for hereditary hemochromatosis is reasonable.
Citations & further reading
Camaschella, NEJM 2015 — Iron deficiency anemia — PMID 25946282. Ferritin < 30 ng/mL is highly specific for iron deficiency; symptomatic deficiency can occur up to ~50 ng/mL.
Adams et al., NEJM 2005 — HFE hemochromatosis — PMID 15858186. HFE C282Y homozygosity is the most common cause of hereditary iron overload in people of Northern European descent.
This page is informational and not medical advice, diagnosis or treatment. Discuss lab results with a qualified healthcare professional before changing diet, supplements or medication.