In a patient with total iron‑binding capacity 311 µg/dL, serum iron 85 µg/dL, transferrin saturation 27 %, and ferritin 37 ng/mL, what is the recommended management?

Iron Deficiency Diagnosis and Management

Your patient has absolute iron deficiency requiring oral or intravenous iron supplementation. 1

Laboratory Interpretation

Your patient's iron panel demonstrates classic absolute iron deficiency:

• Transferrin saturation of 27% is above the diagnostic threshold of <20% for absolute iron deficiency, but ferritin of 37 ng/mL is below the 100 ng/mL threshold, confirming depleted iron stores 2, 1
• The elevated TIBC of 311 µg/dL reflects increased transferrin production as the body attempts to maximize iron-binding capacity in response to low iron stores 1, 3
• Serum iron of 85 µg/dL with ferritin <100 ng/mL indicates insufficient iron stores despite seemingly adequate circulating iron 1
• This pattern represents early iron deficiency where stores are depleted (low ferritin) but transferrin saturation has not yet fallen below 20% 1, 3

Diagnostic Significance

• Ferritin <100 ng/mL is the critical finding that confirms iron deficiency and mandates treatment, regardless of transferrin saturation being above 20% 2, 1
• In the absence of inflammation (which you should confirm with CRP), ferritin <30 ng/mL definitively confirms iron deficiency, and your patient's ferritin of 37 ng/mL is only marginally above this threshold 1
• TIBC increases when serum iron concentration and stored iron are low, and your patient's TIBC of 311 µg/dL reflects this compensatory mechanism 1, 3

Mandatory Workup Before Treatment

Identify the source of iron loss—iron deficiency rarely occurs without an identifiable cause: 1

• Gastrointestinal bleeding: Perform stool guaiac testing; if positive, endoscopic evaluation is mandatory, particularly in men and postmenopausal women to exclude malignancy 1, 3
• Menstrual blood loss: Assess menstrual history in premenopausal women 1
• Dietary insufficiency: Evaluate for restrictive diets, vegetarian/vegan diets, or malabsorption disorders (celiac disease, inflammatory bowel disease) 1
• Medication-induced: Review NSAID use, which can cause occult GI bleeding 1
• Other sources: Consider blood donation history, high-impact athletic activity causing hemolysis, or chronic kidney disease 1

Additional Laboratory Testing

• Complete blood count (CBC) with hemoglobin, hematocrit, MCV, and reticulocyte count to assess severity of anemia and bone marrow response 1
• C-reactive protein (CRP) to assess for inflammation, which can falsely elevate ferritin and mask iron deficiency 1, 3
• Serum creatinine and estimated GFR to evaluate for chronic kidney disease, which alters iron deficiency diagnostic thresholds 1
• Stool guaiac testing for occult GI blood loss 1

Treatment Recommendations

Oral iron is first-line therapy for uncomplicated iron deficiency: 4

• Ferrous sulfate 324 mg (65 mg elemental iron) once daily on an empty stomach, taken 1 hour before or 2 hours after meals to maximize absorption 4
• Continue treatment for 3-6 months after hemoglobin normalizes to replenish iron stores 1
• Recheck iron panel (ferritin, TSAT, CBC) in 4-8 weeks to assess response to therapy 3

Consider intravenous iron if: 1, 3

• Oral iron is not tolerated due to gastrointestinal side effects
• Malabsorption is present (celiac disease, inflammatory bowel disease, gastric bypass)
• Chronic kidney disease is identified (particularly if GFR <30 mL/min/1.73m²)
• Rapid repletion is needed
• Patient fails to respond to oral iron after 4-8 weeks

Target Goals After Treatment

• Ferritin ≥100 ng/mL to ensure adequate iron stores 2, 1
• Transferrin saturation ≥20% to ensure adequate iron availability for erythropoiesis 2, 3
• Hemoglobin normalization based on age and sex-specific reference ranges 1

Common Pitfalls to Avoid

• Do not assume normal ferritin excludes iron deficiency if inflammation is present—ferritin up to 100 ng/mL may still indicate deficiency in inflammatory states 1, 3
• Do not rely solely on transferrin saturation for diagnosis—your patient's TSAT of 27% might falsely reassure, but the low ferritin confirms deficiency 1, 3
• Do not skip the workup for underlying cause—failing to identify GI malignancy or other serious pathology is a critical error 1
• Do not recheck iron parameters within 4 weeks of IV iron administration if that route is chosen, as circulating iron interferes with assays 3