Iron storage protein — the best single marker of iron status, but an acute phase reactant too.
Ferritin is the intracellular iron-storage protein, and serum ferritin approximates total-body iron stores. It's the single best marker for iron status — better than serum iron or transferrin alone.
Low ferritin (<30) indicates iron deficiency even if hemoglobin is still normal. Very high ferritin (>300 in men, >200 in women without inflammation) can signal iron overload (hereditary hemochromatosis, chronic transfusion, liver disease).
Caveat: ferritin is an acute phase reactant that rises with inflammation, infection, and liver damage. Elevated ferritin with elevated hs-CRP can reflect inflammation rather than true iron stores. If ferritin is high and suspicious, check transferrin saturation to confirm.
Ferritin is influenced by: dietary iron intake, menstrual blood loss (in women), GI bleeding, pregnancy, inflammation (raises it falsely), liver disease, alcohol, and pharmacologic agents — iron supplementation raises it; blood donation lowers it.
Check ferritin on any protocol that might affect RBC production or iron demand — HGH/tesamorelin (can raise hematocrit), high-performance athletes. Low ferritin with fatigue in a menstruating woman is common and correctable with oral iron. Pair with hemoglobin, transferrin saturation, and hs-CRP for full context.
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Start tracking →Informational only — not medical advice. Reference ranges vary by lab and individual context. Work with a licensed provider to interpret your specific results.