Step-by-Step Guide to Interpreting Ferritin
Ferritin interpretation requires a systematic approach that first determines whether you're dealing with iron deficiency (ferritin <45 ng/mL) or iron overload (ferritin elevated), then uses transferrin saturation to distinguish true iron disorders from inflammatory or metabolic causes.
Step 1: Establish the Clinical Context
Before interpreting the ferritin number, document:
- Inflammatory conditions (infection, autoimmune disease, malignancy) - ferritin is an acute phase reactant and will be falsely elevated 1
- Chronic kidney disease - alters ferritin interpretation 1
- Liver disease - releases tissue ferritin independent of iron stores 2, 3
- Metabolic syndrome - causes metabolic hyperferritinemia 4
- Recent medications - SGLT2 inhibitors alter ferritin interpretation; GLP-1 agonists may as well 4
Critical pitfall: Ferritin can be elevated from tissue damage, inflammation, or malignancy even when iron stores are normal or low 5, 3. Never interpret ferritin in isolation.
Step 2: Low Ferritin (<45 ng/mL) - Iron Deficiency Pathway
Use <45 ng/mL as your threshold for iron deficiency, not the outdated <15 ng/mL cutoff 1, 6. This threshold provides 85% sensitivity and 92% specificity for iron deficiency 6.
For anemia (Hb <13 g/dL in men, <12 g/dL in non-pregnant women):
If ferritin <45 ng/mL + anemia = iron deficiency anemia (IDA) 1
Then proceed based on patient demographics:
Men and postmenopausal women: Perform bidirectional endoscopy (EGD + colonoscopy) after testing for H. pylori and celiac disease - strong recommendation 1, 6
Premenopausal women: Conditional recommendation for endoscopy; younger women with heavy menses may reasonably choose empiric iron supplementation first 1
If inflammation is present:
Consider adjunctive tests when ferritin may be falsely elevated by inflammation:
- Transferrin saturation
- Soluble transferrin receptor (sTfR)
- sTfR/log-ferritin index
- C-reactive protein 6
Note: sTfR itself is influenced by inflammation, limiting its utility 4
Step 3: Elevated Ferritin - Use TSAT to Guide Workup
The transferrin saturation (TSAT) is the critical branch point for hyperferritinemia 4, 2, 3.
TSAT ≥50% (males) or ≥40% (females) - Suspect True Iron Overload
This pattern suggests the hepcidin-ferroportin axis is allowing excessive iron absorption 4, 7.
Workup sequence:
- HFE genotyping for hereditary hemochromatosis (C282Y, H63D mutations) 4, 2, 7
- Hepatic MRI (T2* or R2 sequences) to quantify liver iron concentration 2
- If confirmed hemochromatosis: therapeutic phlebotomy 7
TSAT <50% (males) or <40% (females) - Non-Iron Overload Causes
Prioritize these evaluations:
Liver function tests (ALT, AST) - hepatocellular injury releases ferritin 2, 3
Inflammatory markers - infection, autoimmune disease, malignancy 4, 3
Metabolic evaluation - metabolic syndrome causes hyperferritinemia via the Valenti consensus criteria 4
Extremely high ferritin (>10,000 μg/L) - consider hemophagocytic lymphohistiocytosis (HLH):
Step 4: Special Populations
Chronic kidney disease patients:
- Standard ferritin thresholds don't apply
- Ferritin <12 μg/L indicates absolute iron deficiency 5
- Levels >15 μg/L may still be insufficient for erythropoietin-stimulated erythropoiesis 5
Older adults (≥70 years):
- Reference ranges are higher: 23-741 μg/L (men), 19-440 μg/L (women) using Abbott Alinity platform 8
- Low ferritin in older men associated with increased GI bleeding and GI cancer risk 8
Children (preadolescent):
- Ferritin lowest at 1.5 years (lower limit 5-6 ng/mL), then gradually increases 9
- Age-specific curves essential for interpretation 9
Step 5: Confirm Iron Repletion After Treatment
Target ferritin >100 ng/mL to confirm restored iron stores 1. Simply normalizing hemoglobin is insufficient - you must document adequate iron reserves to prevent recurrence.