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Ferritin-to-Iron Status Calculator

See whether your ferritin means depleted, adequate or excess iron stores, with an inflammation adjustment.

How it is calculated

The tool compares serum ferritin (ferritin, ng/mL) with a cut-off that depends on sex and on CRP (mg/L). The lower limit is 15 for women and 30 for men; the upper limit is 150 for women and 400 for men. If CRP is above 5, inflammation is treated as present and the deficiency cut-off rises to 70 ng/mL for everyone. Below the cut-off the result is iron deficiency; from the cut-off up to 100 ng/mL it is borderline; from 100 up to the upper limit it is adequate; above the upper limit it is high. An empty CRP field counts as 0, and any sex other than female is read as male. Negative ferritin or CRP shows no result. Other labs and guidelines use different cut-offs, so the category is a screening label, not a diagnosis.

Worked example

A woman has ferritin 22 ng/mL and CRP 8 mg/L. CRP is above 5, so the cut-off moves from 15 to 70 ng/mL, and the tool prints it as an inflammation-adjusted threshold. Since 22 is below 70, the status is "Iron deficiency: ferritin is below the threshold, iron stores are depleted." The reference range shown for comparison is 15 - 150 ng/mL (female). With CRP of 2 instead, the cut-off would stay at 15 and the same ferritin would fall in the borderline band.

Try this example →

Common mistakes

  • Reading 22 ng/mL as normal without entering CRP: with CRP above 5 mg/L the cut-off is 70, so the category changes from borderline to deficiency.
  • Entering ferritin in a different unit from another report: the tool expects ng/mL (the numbers are the same for µg/L, but not for pmol/L).
  • Entering CRP in mg/dL instead of mg/L; 0.8 mg/dL is 8 mg/L, which crosses the inflammation threshold.
  • Forgetting to choose the sex: any value other than female is read as male, which shifts the reference range to 30 - 400 ng/mL.
  • Treating a high-ferritin result as proof of iron overload; the tool only says overload, inflammation or liver disease should be considered.

Sources

About this calculator

Serum ferritin reflects the body's stored iron, but interpreting a single number requires two adjustments: sex-specific reference ranges (women's normal ferritin is typically lower than men's due to menstrual iron losses), and a correction for inflammation, since ferritin is also an acute-phase reactant that rises during infection or inflammation independent of actual iron stores — which is why CRP (C-reactive protein) is checked alongside it.

Physicians use inflammation-adjusted ferritin thresholds (commonly, ferritin below roughly 15-30 ng/mL suggests depletion, while very high levels combined with elevated CRP point toward an inflammatory rather than iron-overload cause) to avoid two opposite mistakes: missing iron deficiency in a patient whose inflammation is masking a low result, or misdiagnosing iron overload in a patient whose high ferritin is actually just inflammation. It's a standard step in working up unexplained fatigue, anemia investigations, and chronic disease management.

This calculator takes your ferritin level, sex and CRP and returns an iron status category adjusted for inflammation. The 30 ng/mL (men) and 15 ng/mL (women) lower limits used here are a simplification: WHO 2020 uses below 15 µg/L for adults of either sex, and below 70 µg/L when infection or inflammation is present.

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