In a patient with hemoglobin 11.1 g/dL, serum iron 142 µg/dL, total iron‑binding capacity 400 µg/dL, and transferrin saturation 36%, what is the likely cause of the anemia and what further evaluation is recommended?

Anemia with Normal Iron Studies: Likely Anemia of Chronic Disease

This patient has anemia (Hgb 11.1 g/dL) with normal-to-adequate iron parameters (serum iron 142 µg/dL, transferrin saturation 36%, TIBC 400 µg/dL), which strongly suggests anemia of chronic disease (ACD) or another non-iron-deficiency cause rather than iron deficiency anemia.

Iron Status Interpretation

Your patient's iron studies are not consistent with iron deficiency:

• Transferrin saturation of 36% is well above the threshold for iron deficiency (typically <20% indicates deficiency) 1
• Serum iron of 142 µg/dL is normal-to-elevated (not low as expected in iron deficiency)
• TIBC of 400 µg/dL is at the upper limit of normal but not markedly elevated as typically seen in iron deficiency

In iron deficiency anemia, you would expect:

• Low serum iron
• High TIBC (>400 µg/dL)
• Low transferrin saturation (<16-20%)
• Low ferritin (though you haven't provided this value)

Most Likely Diagnosis: Anemia of Chronic Disease

The combination of anemia with adequate iron stores and normal-to-high transferrin saturation points toward anemia of chronic disease 2. This condition is characterized by:

• Hypoproliferative anemia
• Normal or elevated serum ferritin
• Low-normal to normal serum iron
• Normal or low TIBC
• Normal or mildly reduced transferrin saturation (typically >20%)
• Impaired erythropoietin production and response

Required Further Evaluation

Essential Next Steps:

1. Check serum ferritin - This is the critical missing value. In ACD, ferritin is typically normal or elevated (>100 µg/L), whereas in iron deficiency it would be <45 ng/mL 3

2. Evaluate for underlying chronic conditions:

   • Chronic kidney disease (check creatinine, GFR)
   • Chronic heart failure
   • Inflammatory conditions (check CRP, ESR)
   • Malignancy screening if age-appropriate
   • Chronic infections
   • Autoimmune diseases

3. Consider soluble transferrin receptor (sTfR) if ferritin is elevated and you suspect coexistent iron deficiency 4. An elevated sTfR in the setting of elevated ferritin suggests true iron deficiency masked by inflammation

Important Caveats:

Functional iron deficiency can occur in chronic conditions (particularly CKD and CHF) where ferritin may be elevated but iron utilization is impaired 1. In these specific contexts:

• CKD: Iron deficiency defined as transferrin saturation ≤20% with ferritin ≤100 µg/L (predialysis) or ≤200 µg/L (hemodialysis)
• CHF: Iron deficiency defined as ferritin <100 µg/L and/or transferrin saturation <20%

However, your patient's transferrin saturation of 36% argues against functional iron deficiency in these conditions.

Management Approach

Do not empirically treat with iron supplementation at this time. With transferrin saturation of 36%, iron therapy is unlikely to be beneficial and may cause harm through oxidative stress 5.

Instead:

1. Complete the diagnostic workup (ferritin, inflammatory markers, renal function)
2. Identify and treat the underlying chronic condition
3. Consider erythropoietin-stimulating agents if anemia is due to CKD with inadequate erythropoietin production
4. Reserve iron therapy only if ferritin is definitively low (<45 ng/mL) or if functional iron deficiency is confirmed in specific disease contexts (CKD, CHF) with appropriate specialist consultation 1