Ferritin Correction for Inflammation Calculator
Ferritin Correction for Inflammation Calculator
Apply the right ferritin threshold for a patient with raised CRP, where the usual 30 µg/L cut-off no longer excludes iron deficiency.
Ferritin Correction for Inflammation
Ferritin + CRP → thresholdFerritin 65 µg/L, CRP 12 mg/L
The thresholds
CRP > 5 mg/L → ferritin < 100 µg/L = deficient
- CRP 5 mg/L
- the conventional cut-off for a detectable acute-phase response
- 100 µg/L
- the raised threshold recommended when inflammation is present
Worked example
Ferritin 65 µg/L, CRP 12 mg/L
CRP 12 mg/L is above 5, so the threshold rises to 100 µg/L
Ferritin 65 µg/L is below that threshold → iron deficiency likely
Ferritin thresholds by inflammatory state
| CRP | Deficient | Indeterminate | Adequate |
|---|---|---|---|
| ≤ 5 mg/L | < 30 µg/L | 30 – 100 µg/L | > 100 µg/L |
| > 5 mg/L | < 100 µg/L | 100 – 300 µg/L | > 300 µg/L |
Why the threshold moves
Ferritin is simultaneously the best available marker of iron stores and a positive acute-phase reactant. Interleukin-6 drives hepatic ferritin synthesis during any inflammatory episode, so the same iron stores produce a higher measured ferritin in an inflamed patient than in a well one. Applying the usual 30 µg/L cut-off to that patient will miss real iron deficiency.
The asymmetry is the key to using it safely. Inflammation raises ferritin and never lowers it, so a low result is always trustworthy — a ferritin of 20 µg/L means absent stores whether CRP is 2 or 200. It is only the normal and high results that become uninterpretable, and that is where the raised threshold applies.
Several approaches exist for handling this. The simplest, used in most gastroenterology and cardiology guidelines, raises the cut-off to 100 µg/L when inflammation is present. More sophisticated methods such as the BRINDA regression adjust ferritin continuously against CRP and AGP for population surveys. For an individual patient, the raised threshold plus a transferrin saturation is usually enough.
Frequently asked questions
What ferritin level means iron deficiency if CRP is high?
Below 100 µg/L rather than the usual 30 µg/L. Inflammation raises ferritin, so the standard threshold misses real deficiency in inflamed patients.
Can inflammation make ferritin falsely low?
No. The acute-phase response only raises ferritin. That is why a low ferritin is diagnostic whatever the CRP, while a normal one may not be.
What if ferritin is between 100 and 300 with inflammation?
Ferritin cannot answer the question in that range. Use transferrin saturation — under 20% supports deficiency — or the sTfR-ferritin index, which is unaffected by inflammation.
Which CRP cut-off should I use?
5 mg/L is the conventional threshold for a detectable acute-phase response. Some protocols use 10 mg/L, and others add alpha-1-acid glycoprotein to catch chronic low-grade inflammation.
Related calculators
References
- WHO. Serum ferritin concentrations for the assessment of iron status. Geneva, 2020.
- Namaste SM et al. Adjusting ferritin concentrations for inflammation: BRINDA project. Am J Clin Nutr. 2017;106(Suppl 1):359S–371S.
- Ponikowski P et al. ESC Guidelines for heart failure — iron deficiency definition.