Ferritin Testing: Your Iron Storage Report Card
Content last reviewed 2026-09-12 · Educational information — not medical advice
Quick answer
Ferritin measures stored iron — the single most informative iron-status number available. Below 30 means genuinely empty stores even when hemoglobin looks fine; high readings need CRP context because inflammation inflates ferritin independently.
Why ferritin beats serum iron
Serum iron swings meal-to-meal and hour-to-hour; ferritin reflects WAREHOUSE INVENTORY, stable across weeks. A ferritin of 12 means empty shelves regardless of today's lunch. The catch cutting one direction: ferritin doubles as an acute-phase reactant, so inflammation, liver disease, and metabolic syndrome all inflate it — pairing with CRP separates true overload from inflammatory masking.
The deficiency spectrum
<15: absent stores · 15–30: depleted (treat-worthy especially symptomatic) · 30–100: adequate-ish · 100+ with normal CRP: replete or overloaded · 300–1000+: investigate hemochromatosis/liver/inflammation with transferrin saturation alongside.
Symptoms at 'normal-looking' levels
Restless legs, hair shedding, brittle nails, ice-craving (pagophagia), exercise intolerance, and plain exhaustion occur at ferritin 20–50 in many patients — above lab lower-limits but below tissue-optimal. Trial repletion under guidance frequently transforms energy; this is the most common 'my labs are normal but I feel terrible' story in medicine.
Found low — next steps that matter
Men and postmenopausal women with low ferritin need SOURCE HUNTING (GI evaluation), not just supplementation — occult bleeding hides somewhere until proven otherwise. Premenopausal women get menstruation as default explanation after basic screening. Recheck 8–12 weeks into repletion to confirm trajectory.
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Frequently asked questions
Can I test ferritin while taking iron?
Yes — ongoing oral iron modestly raises readings; consistent timing across tests keeps trends interpretable.
Is ferritin 150 too high?
Mildly elevated readings usually trace to inflammation or fatty liver rather than iron overload — saturation percentage (>45%) is the hemochromatosis discriminator.