November 2024
Ampath | ampath.co.za
1. Updated Reference Ranges for Ferritin and Transferrin Saturation
- Lower reference limits have changed:
- Ferritin: Now 30 µg/L (was previously lower)
- Transferrin saturation (TS): Now 20% in all adults
- Ferritin units updated from ng/mL to µg/L to align with SI standards
- Changes reflect current expert consensus, correcting previously outdated ranges
2. Interpreting Iron Studies in the Context of Inflammation
- Ferritin is a positive acute-phase reactant → increases with inflammation or infection
- Transferrin is a negative acute-phase protein → decreases with inflammation
Key Considerations:
- Iron deficiency (ID) may be masked in chronic inflammation (e.g. obesity, diabetes, renal or heart failure, IBD)
- Ferritin <100 µg/L in presence of low TS (<20%) suggests ID, even during inflammation
- Ferritin >100 µg/L can still indicate ID if TS remains low
To Confirm ID When Ferritin Appears Normal:
- Soluble transferrin receptor (STFR) → increased
- Reticulocyte haemoglobin content (RET) → decreased
3. Vitamin B12 and Folate: Interpretation Guidelines
When to Test:
- Always assess vitamin B12 in patients with megaloblastic anaemia, especially if neurological symptoms are present
- Check folate in high-risk groups:
- GI disorders
- Excessive alcohol use
- Folate-poor diets
Interpreting Borderline Results:
- If B12 or folate is borderline low, test homocysteine and possibly methylmalonic acid (MMA)
Diagnostic Patterns:
- ↑ Homocysteine + ↑ MMA → Vitamin B12 deficiency
- ↑ Homocysteine + Normal MMA → Folate deficiency
Additional B12 Testing Insights:
- False-normal B12 can occur if transcobalamin is elevated (seen in malignancy, liver/kidney disease, autoimmune conditions)
- Use homocysteine to support clinical diagnosis
- Spurious low B12 (non-deficient) may occur in:
- Multiple myeloma
- HIV
- Pregnancy
- Oral contraceptives
- Phenytoin use
4. Serum vs Red Cell Folate – Which to Use?
✅ Serum Folate (Preferred test):
- Reflects recent intake but remains valid unless taking supplements
- Detects early deficiency
- More reliable than red cell folate in:
- B12 deficiency (avoids "folate trapping")
- Pregnancy (for neural tube defect risk)
- Haemodialysis (before dialysis)
- Chemotherapy planning (capecitabine toxicity risk)
✅ Red Cell Folate (For long-term folate status):
Use in specific situations:
- After haemodialysis
- Assessing long-term neural tube defect (NTD) risk in non-pregnant individuals
- Unresolved anaemia cases
📌 Need help? Contact your local Ampath representative for test selection or interpretation support.
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