Severe Iron Deficiency Requires Intravenous Iron Therapy
With serum iron 15 µg/dL, transferrin saturation 4%, and ferritin 6 ng/mL, this patient has severe absolute iron deficiency and should receive intravenous iron infusion. This represents profound depletion of iron stores that warrants parenteral therapy.
Diagnostic Interpretation
Your patient's laboratory values indicate absolute iron deficiency by all standard criteria:
- Ferritin 6 ng/mL is severely depleted (normal threshold >30 ng/mL for adults, >100 ng/mL in cancer/CKD contexts) 1
- Transferrin saturation 4% is critically low (normal >20%, absolute deficiency defined as <15%) 1
- Serum iron 15 µg/dL confirms inadequate circulating iron 1
These values meet criteria for absolute iron deficiency across multiple guideline frameworks, including NCCN (ferritin <30 ng/mL, TSAT <15%) 1 and KDIGO (TSAT ≤20%, ferritin ≤100 ng/mL) 1.
Why Intravenous Iron is Indicated
Intravenous iron should be used when:
- Severe depletion exists (ferritin <30 ng/mL qualifies) 1
- Rapid correction is needed to prevent symptomatic anemia progression 1, 2
- Oral iron has failed or is unlikely to work given the severity of deficiency 1, 3
The 2024 AGA guidelines specifically recommend IV iron "if ferritin levels do not improve with a trial of oral iron, or the patient has a condition in which oral iron is not likely to be absorbed" 1. With ferritin this profoundly low (6 ng/mL), oral supplementation alone would require months to replete stores 4.
Treatment Approach
For absolute iron deficiency without active inflammation:
- First-line: Consider a trial of oral iron (ferrous sulfate 100-200 mg elemental iron daily or every other day) with vitamin C supplementation 1, 4
- Preferred approach given severity: Proceed directly to IV iron using high-dose formulations that allow 1-2 infusion completion 1, 2
Specific IV iron dosing:
- Total iron deficit replacement: typically 1000 mg for absolute deficiency 1
- Modern formulations (ferric carboxymaltose, iron isomaltoside) allow single-dose or two-dose regimens 1, 2
- Iron sucrose or ferric gluconate require multiple smaller doses (100-200 mg per session) 5, 6
Clinical Context Matters
Determine the underlying cause:
- If cancer-related: IV iron is strongly recommended for absolute deficiency (ferritin <100 ng/mL) in patients on chemotherapy 1
- If CKD-related: IV iron is indicated when TSAT ≤20% and ferritin ≤100 ng/mL 1
- If GI blood loss: Address the source while repleting with IV iron 1
- If malabsorption: IV iron is preferred over oral 1
Safety Considerations
IV iron is safe with modern formulations:
- True anaphylaxis risk is very rare (<1:250,000 administrations) 1
- Most reactions are complement activation-related pseudo-allergy (infusion reactions), not true allergy 1, 2
- Premedication protocols (diphenhydramine, cimetidine, dexamethasone) further reduce reaction risk 3
Monitor for hypophosphatemia: Ferric carboxymaltose specifically can cause hyperphosphaturic hypophosphatemia in 50-74% of patients, potentially leading to bone complications 2. Consider alternative formulations or phosphate monitoring if using this agent.
Follow-Up Assessment
Recheck iron studies 8-10 weeks after treatment:
- Expected increases: hemoglobin +1-2 g/dL, ferritin +250-450 ng/mL, TSAT +8-14% 5, 4
- Do not recheck ferritin immediately after IV iron as levels are falsely elevated 1
- If no response, investigate for ongoing blood loss, malabsorption, or inflammatory conditions 1
Common pitfall: Failing to identify and treat the underlying cause of iron deficiency. With ferritin this low, investigate for GI blood loss, malabsorption (celiac disease), menorrhagia, or dietary insufficiency 1, 4.