In a patient with mild normocytic to borderline macrocytic anemia (hemoglobin 11.3 g/dL, hematocrit 37.7 %, mean corpuscular volume 99 fL), thrombocytopenia (platelet count 110 ×10³/µL), iron studies showing low serum iron, low total iron‑binding capacity, high transferrin saturation and elevated ferritin, an elevated blood urea nitrogen (BUN) with a high BUN/creatinine ratio, mild eosinophilia, normal thyroid function, adequate folate and vitamin B12, sufficient vitamin D, and current use of naproxen, what is the most likely diagnosis and what management steps should be taken?

Anemia of Chronic Disease with Possible Gastrointestinal Blood Loss

This patient most likely has anemia of chronic disease (ACD) with possible occult gastrointestinal bleeding related to naproxen use, and requires immediate discontinuation of the NSAID, gastrointestinal evaluation, and assessment for inflammatory conditions.

Key Diagnostic Features

The iron studies reveal a paradoxical pattern inconsistent with simple iron deficiency:

• Low TIBC (233.6 µg/dL) and low UIBC (140 µg/dL) indicate suppressed transferrin production, characteristic of chronic inflammation 1
• Elevated ferritin (337.3 ng/mL) with high transferrin saturation (40%) suggests anemia of chronic disease rather than absolute iron deficiency 1
• In the absence of inflammation, ferritin >100 µg/L essentially excludes absolute iron deficiency 1, 2

The elevated BUN (40 mg/dL) with high BUN/creatinine ratio (40) strongly suggests upper gastrointestinal bleeding, as blood is digested and absorbed, raising BUN disproportionately to creatinine 3.

Anemia Classification and Mechanism

• Borderline macrocytic anemia (MCV 99 fL, hemoglobin 11.3 g/dL) falls into the normocytic-to-macrocytic range 4
• The low MCHC (30.0 g/dL) and elevated RDW (16.6%) suggest a mixed picture with some iron-restricted erythropoiesis despite adequate iron stores 2
• Thrombocytopenia (110 × 10³/µL) raises concern for bone marrow involvement, chronic disease, or medication effect 3

Critical Management Steps

1. Immediate Medication Review

Discontinue naproxen immediately 3:

• NSAIDs cause occult GI blood loss and can produce anemia through multiple mechanisms 3
• Naproxen specifically causes eosinophilia (present at 8.3%) and can affect erythropoiesis 3
• The FDA label explicitly warns that "anemia is sometimes seen in patients receiving NSAIDs, including naproxen, due to fluid retention, occult or gross GI blood loss, or an incompletely described effect upon erythropoiesis" 3

2. Gastrointestinal Evaluation

Pursue upper and lower GI tract investigation 5:

• The elevated BUN/creatinine ratio strongly suggests upper GI bleeding 5
• Upper endoscopy should be performed to exclude gastric cancer, peptic ulcer disease, or angiodysplasia 5
• Colonoscopy or imaging should evaluate for colonic sources of blood loss 5
• Test stool for occult blood 4

3. Inflammatory Disease Assessment

Measure inflammatory markers (CRP, ESR) to clarify the anemia mechanism 1:

• With ferritin >100 µg/L and transferrin saturation >20%, anemia of chronic disease is likely if inflammation is present 1
• The diagnostic criteria for ACD in the presence of inflammation are ferritin >100 µg/L and transferrin saturation <16% 1
• This patient's transferrin saturation of 40% argues against functional iron deficiency but the low TIBC suggests chronic inflammation 1

4. Evaluate for Underlying Chronic Conditions

Screen for conditions associated with ACD:

• Inflammatory bowel disease: Given the anemia pattern and potential GI involvement 1, 2
• Chronic kidney disease: The GFR is borderline (75 mL/min/1.73m² for non-African American), which can contribute to anemia 2, 6
• Malignancy: Unexplained anemia with thrombocytopenia warrants evaluation 4
• Autoimmune conditions: Mild eosinophilia may suggest underlying inflammatory disease 3

5. Reticulocyte Count

Order a reticulocyte count (corrected for anemia) to assess bone marrow response 4:

• A low reticulocyte index (<2.0) indicates decreased RBC production, suggesting bone marrow dysfunction, nutritional deficiency, or ACD 4
• A normal or elevated reticulocyte index would suggest hemolysis or blood loss with adequate marrow response 4

6. Peripheral Blood Smear Review

Visual examination of the peripheral smear is critical 4:

• Confirms RBC size, shape, and color abnormalities 4
• May reveal features of hemolysis, dysplasia, or other hematologic disorders 4

Iron Supplementation Decision

Do NOT initiate iron supplementation at this time 1:

• Ferritin >100 µg/L with transferrin saturation 40% indicates adequate iron stores 1, 2, 1
• Iron supplementation is contraindicated when ferritin is elevated without confirmed deficiency 1
• In the presence of inflammation, ferritin <100 µg/L combined with transferrin saturation <16% would be required to diagnose iron deficiency 1

Common Pitfalls to Avoid

• Do not interpret elevated ferritin as iron overload alone—it is an acute phase reactant and may be elevated in inflammation 1
• Do not assume iron deficiency based solely on anemia and low hemoglobin—the iron panel must be interpreted in the context of inflammation 1
• Do not overlook the significance of the elevated BUN/creatinine ratio—this is a red flag for upper GI bleeding 5
• Do not continue naproxen—NSAIDs are a well-established cause of GI blood loss and anemia 3

Monitoring Plan

• Recheck CBC in 2-4 weeks after naproxen discontinuation 3
• Monitor hemoglobin and platelet count for improvement 3
• Reassess iron studies after treating any identified inflammatory condition 1
• If anemia persists despite addressing reversible causes, consider hematology referral for bone marrow evaluation 4