Serum ferritin value and its prediction
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Serum Ferritin: Values and Predictive Significance
1. What Is Serum Ferritin?
Ferritin is a ubiquitous intracellular iron-storage protein present in nearly all cells. A small fraction leaks into the circulation; serum ferritin is in equilibrium with storage ferritin in reticuloendothelial tissues, making it the most clinically useful surrogate marker of total body iron stores.
"1 μg/L of serum ferritin ≈ 8–10 mg of storage iron" — Henry's Clinical Diagnosis and Management by Laboratory Methods
The measurement is performed by sandwich immunoassay (ELISA, chemiluminescent platforms). First described immunometrically in 1972 (Addison et al.), it has since been incorporated into virtually all automated immunoassay analysers.
2. Reference Values
| Population | Reference Interval |
|---|---|
| Adult general | 12–300 μg/L |
| Men | Higher end (stored iron ~1000 mg) |
| Premenopausal women | Lower end (menstrual losses) |
| Postmenopausal women | Rises to male-comparable levels |
| Children 6 months–15 years | Somewhat lower than adults |
| Neonates/early infancy | Transiently high |
Key caveats from Tietz Textbook of Laboratory Medicine (7th ed.):
- Ferritin does not display diurnal variation (unlike serum iron and TSAT, which vary up to 30% throughout the day).
- Reference intervals differ between laboratories, depending on whether they use 2.5–97.5 or 5–95 centile definitions and whether the reference population includes iron-depleted individuals or subjects with obesity-associated hyperferritinemia.
3. Predictive Cut-offs for Iron Deficiency (ID)
Ferritin falls before haemoglobin, MCV, or serum iron change — making it the earliest and most sensitive marker of iron depletion.
WHO definitions (widely cited, low–moderate certainty of evidence):
| Condition | Cut-off |
|---|---|
| ID (children <5 years) | < 12 μg/L |
| ID (children >5 years, adolescents, adults) | < 15 μg/L |
| ID with concurrent inflammation (children <5 years) | < 30 μg/L |
| ID with concurrent inflammation (≥5 years/adults) | < 70 μg/L |
Guyatt et al. systematic review (1990, 55 studies, gold standard meta-analysis):
| Decision | Cut-off | Interpretation |
|---|---|---|
| Rule in IDA | ≤ 15 μg/L | High specificity (98%) |
| Rule out IDA (general population) | > 40 μg/L | High negative predictive value |
| Rule out IDA (inflammatory/liver/malignancy) | > 70 μg/L | Adjusted NPV for inflamed patients |
The threshold of 15 μg/L in non-inflammatory states:
- Specificity: 98% (diagnostic of ID when low)
- Sensitivity: 75%
Raising the threshold to 30 μg/L in premenopausal women (Hallberg et al.):
- Sensitivity improves to 93%
- Specificity decreases to 75%
These cut-offs remain the basis of the 2011 British Society of Gastroenterology guideline and the 2020 American Gastroenterological Association guideline. — Tietz, 7th ed.
4. Ferritin as an Acute-Phase Reactant (the key confounder)
Ferritin is a positive acute-phase reactant. In inflammation, infection, malignancy, and hepatocellular disease, serum ferritin rises disproportionately to actual iron stores. This is the most important limitation of its predictive use:
- In inflammatory states, true IDA can coexist with normal or elevated ferritin.
- Practically: a ferritin < 50–60 μg/L in inflamed patients is likely to respond to iron therapy (Henry's).
- Hypothyroidism and ascorbate deficiency may lower ferritin independent of iron stores, further complicating interpretation.
5. Prediction of Iron Overload
WHO thresholds for iron overload:
| Population | Ferritin threshold |
|---|---|
| Healthy males / postmenopausal women | > 200 μg/L |
| Premenopausal females | > 150 μg/L |
| Unhealthy individuals | > 500 μg/L |
In hereditary haemochromatosis (HFE-HH): serum ferritin is highly sensitive for iron overload when used alongside transferrin saturation (TSAT). A TSAT >45–60% combined with elevated ferritin is the standard screening combination. A marked ferritin elevation (>1000 μg/L) with normal TSAT may still represent significant iron overload (e.g., ferroportin disease) and warrants further work-up.
Ferritin is also used to monitor response to:
- Phlebotomy therapy (haemochromatosis)
- Iron chelation therapy (thalassaemia, transfusional overload)
6. Summary of Ferritin's Predictive Role Across Clinical Scenarios
| Clinical Scenario | Ferritin Behaviour | Predictive Use |
|---|---|---|
| Uncomplicated iron deficiency | ↓ early, even before anaemia | Best single test; rules in ID at <15 μg/L |
| Iron deficiency with inflammation | May be normal or ↑ | Use cut-off >70 μg/L to rule out ID |
| Hereditary haemochromatosis | ↑ | Sensitive marker; use with TSAT |
| Anaemia of chronic disease | Normal or ↑ | Does not reflect true iron status |
| Hepatocellular disease | ↑ disproportionately | Unreliable for iron stores |
| Malignancy | ↑ (tumour-associated) | Not reliable for iron assessment |
| Ferritin >1000 μg/L (any cause) | Haemophagocytic lymphohistiocytosis (HLH) alarm threshold | Combined with other HLH criteria |
| CKD/dialysis patients | Targets: >200 μg/L on dialysis; >100 μg/L in ND-CKD | Guides ESA and IV iron therapy |
7. Analytical Considerations
- Inter-assay variability exists because ferritin immunoassays from different manufacturers may not all be calibrated to the current WHO 3rd International Standard — a source of clinically meaningful bias.
- Assay drift and lack of harmonization mean that cut-offs derived from older studies may not translate directly to results from modern platforms (Tietz, 7th ed.).
Sources:
- Tietz Textbook of Laboratory Medicine, 7th Edition — Methods for Serum Ferritin, Body Iron Distribution
- Henry's Clinical Diagnosis and Management by Laboratory Methods — Serum Ferritin Levels, Laboratory Features
- Katzung's Basic and Clinical Pharmacology, 16th Edition — Iron Storage
- Brenner and Rector's The Kidney — Markers of Iron Status in CKD
- Recent reviews: Ruivard & Lobbes (2023, PMID 37507250); Melas & Stål (2024, PMID 39411810); Anders & Sorda (2026, PMID 41961610)
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