What is the likely diagnosis and appropriate management for a patient with serum iron 30 µg/dL, ferritin 118 ng/mL, transferrin saturation (TSAT) 18 %, total iron‑binding capacity (TIBC) 169 µg/dL, and unsaturated iron‑binding capacity (UIBC) 139 µg/dL?

Functional Iron Deficiency Despite Normal Ferritin

This patient has functional iron deficiency (FID) characterized by low transferrin saturation (18%) despite normal-to-elevated ferritin (118 ng/mL), requiring investigation for underlying inflammatory conditions and consideration of intravenous iron therapy if oral supplementation fails.

Laboratory Interpretation

Your iron panel reveals a discordant pattern:

• Transferrin saturation of 18% is below the diagnostic threshold of 20%, indicating insufficient iron availability for erythropoiesis 1
• Ferritin of 118 ng/mL appears normal but may be falsely elevated by inflammation, as ferritin is an acute-phase reactant 2
• Low TIBC (169 µg/dL) suggests possible inflammation suppressing iron mobilization, rather than the elevated TIBC typically seen in absolute iron deficiency

This pattern is diagnostic of functional iron deficiency when TSAT <20% occurs with ferritin 100-300 µg/L 2. The inflammation-driven increase in hepcidin restricts dietary iron uptake and sequesters iron in storage sites, making it unavailable despite adequate stores 2.

Underlying Conditions to Investigate

Prioritize evaluation for these specific inflammatory conditions where FID is prevalent:

• Chronic heart failure (40-70% have iron deficiency defined as ferritin <100 µg/L and/or TSAT <20%) 1
• Inflammatory bowel disease (one-third have iron deficiency; ferritin up to 100 µg/L may still reflect deficiency with inflammation) 1
• Chronic kidney disease (absolute iron deficiency defined as TSAT ≤20% with ferritin ≤100 µg/L in predialysis patients) 1
• Celiac disease (impairs iron absorption) 3
• Helicobacter pylori infection (common cause requiring noninvasive testing) 4

Gastrointestinal Evaluation

If no inflammatory condition is identified, investigate for occult blood loss:

• Bidirectional endoscopy is indicated to exclude gastrointestinal pathology, particularly if the patient is male or postmenopausal female 4
• Noninvasive testing for H. pylori and celiac disease should be performed as both commonly cause iron deficiency 4
• In premenopausal women with heavy menstrual bleeding, treating the bleeding source while providing iron supplementation is reasonable before invasive testing 4

Management Algorithm

First-Line: Oral Iron Supplementation

Start with oral ferrous salts (ferrous sulfate, fumarate, or gluconate) as they are least expensive and equally effective 3:

• Every-other-day dosing improves absorption compared to daily dosing 4
• Take on empty stomach when possible; if not tolerated, take with meals containing meat protein 3
• Add 500 mg vitamin C to enhance absorption even with calcium or fiber present 3
• Reassess in 2-4 weeks for response 4

Common pitfall: Approximately 50% of patients have poor adherence due to gastrointestinal side effects (nausea, abdominal pain, constipation) 3, 4

Second-Line: Intravenous Iron

Switch to IV iron if:

• Oral iron is not tolerated or ineffective after 2-4 weeks 4
• Patient has chronic heart failure (IV iron has proven prognostic benefit; oral iron should be avoided due to poor absorption from gut edema) 1
• Patient has moderate-to-severe anemia with IBD (Hb <100 g/L) 1
• Patient has CKD on dialysis 1

Hypersensitivity to newer IV iron formulations is rare (<1%) 4

Treatment Targets

• Hemoglobin: 10-12 g/dL or normalization 5
• Ferritin: >100 µg/L (but not exceeding 500-800 µg/L in CKD to avoid iron overload) 5
• TSAT: ≥20% 5

Monitoring

• Every 3 months for at least one year after correction in IBD patients 1
• Periodic surveillance thereafter in at-risk groups 2

Critical Context

The weak correlation between hemoglobin and TSAT in inflammatory conditions (compared to non-inflammatory states) 6 underscores why both ferritin and TSAT must be measured together in these patients 2. Using ferritin alone would have missed your diagnosis, as the standard threshold of <30 µg/L does not apply when inflammation is present 2.