In a 73-year-old man with hemoglobin 12.8 g/dL, hematocrit 37.5 %, transferrin saturation 19 %, serum iron 61 µg/dL, total iron‑binding capacity 262 µg/dL, ferritin 37 ng/mL, and glomerular filtration rate 65 mL/min/1.73 m², what does this pattern indicate and what should be the next step in management?

Iron Deficiency Anemia with Chronic Kidney Disease Stage 3a

This patient has iron deficiency anemia (IDA) in the setting of chronic kidney disease (CKD) stage 3a, and the next step is to initiate oral iron supplementation with ferrous sulfate 300 mg three times daily while investigating for gastrointestinal blood loss.

Laboratory Pattern Indicates Iron Deficiency

Your patient's laboratory values demonstrate classic iron deficiency:

• Ferritin 37 ng/mL is below the threshold of 100 ng/mL that defines absolute iron deficiency in CKD patients 1
• Transferrin saturation 19% (calculated as 61/262 × 100) is below the 20% threshold, confirming iron-restricted erythropoiesis 1
• Hemoglobin 12.8 g/dL is below the WHO threshold of 13 g/dL for men, meeting criteria for anemia 1, 2
• GFR 65 mL/min/1.73 m² places him in CKD stage 3a, where anemia prevalence increases significantly 1

The combination of ferritin <100 ng/mL and transferrin saturation <20% definitively establishes **absolute iron deficiency** 1, 3. This is not anemia of chronic disease, which would show ferritin >100 ng/mL with low transferrin saturation 1, 4.

Why This Matters in CKD Stage 3a

At GFR 65 mL/min/1.73 m², your patient is at the threshold where anemia becomes increasingly common. Mean hemoglobin levels begin to decline consistently when GFR falls below 60 mL/min/1.73 m² 1. In men specifically, the slope of hemoglobin decrease is steeper at any given level of kidney function 1.

The ferritin of 37 ng/mL is particularly concerning because it indicates depleted iron stores 1. Even though his hemoglobin is only mildly reduced, iron deficiency at this level will worsen as kidney function declines and erythropoietin production decreases.

Immediate Management: Oral Iron Supplementation

Start ferrous sulfate 300 mg orally three times daily immediately 5. The goal is to:

• Replenish depleted iron stores (target ferritin >100 ng/mL) 5
• Achieve transferrin saturation >20% 5
• Continue supplementation for at least 3 months, not just until hemoglobin normalizes 5

After 3 months, recheck ferritin and transferrin saturation to assess iron store repletion 5. If oral iron fails after 3 months or the patient cannot tolerate it, consider intravenous iron 5.

Critical Next Step: Investigate for GI Blood Loss

In a 73-year-old man with iron deficiency, gastrointestinal blood loss is the most common cause and must be excluded 1. Even though he has CKD, you cannot assume the anemia is solely due to kidney disease when iron deficiency is present.

Specific workup required:

• Upper and lower endoscopy should be considered, particularly in adults >50 years 5
• Check fecal occult blood 5
• Obtain detailed history of:
  • NSAID use (stop if possible) 1
  • Aspirin or anticoagulant use 1
  • GI symptoms (though these rarely correlate with findings) 1
• Small bowel biopsies during upper endoscopy to screen for celiac disease, which causes IDA in 2-3% of cases 1

The British Society of Gastroenterology guidelines emphasize that investigation should be considered at any level of anemia in the presence of iron deficiency, especially in men, as colorectal cancer can present with mild anemia 1.

Common Pitfalls to Avoid

1. Do not assume the anemia is solely due to CKD when iron deficiency is documented. GI pathology must be excluded first 1.

2. Do not stop iron supplementation prematurely. Ferritin must reach >100 ng/mL to ensure adequate stores; stopping when hemoglobin normalizes leads to rapid recurrence 5.

3. Do not use ferritin alone to guide therapy. Always assess transferrin saturation simultaneously, as ferritin can be falsely elevated by inflammation 1, 4.

4. Do not delay investigation because the anemia is "mild." Mild anemia is not less indicative of serious pathology than severe anemia 1.

Monitoring Plan

• Recheck CBC, ferritin, and transferrin saturation after 3 months of oral iron 5
• Monitor kidney function (GFR, creatinine) every 3-6 months given CKD stage 3a
• If ferritin continues to decline despite supplementation, this indicates ongoing iron loss and mandates more aggressive GI investigation 5
• Consider IV iron if oral iron fails or is not tolerated after 3 months 5

When to Consider Erythropoiesis-Stimulating Agents

At this stage, ESAs are not indicated. Your patient's hemoglobin is 12.8 g/dL, and ESA therapy is typically reserved for patients with hemoglobin <10 g/dL in CKD 6. First, correct the iron deficiency, as ESAs cannot work effectively without adequate iron stores 1, 6.