Yes, bone marrow iron stores are typically normal or even increased in anemia caused by low erythropoietin production due to chronic kidney disease.
In CKD-related anemia from EPO deficiency, bone marrow iron stores remain adequate because the primary problem is insufficient erythropoietin to stimulate red blood cell production, not a lack of available iron. This creates a situation where iron accumulates in storage sites (including bone marrow macrophages) because it cannot be effectively utilized for erythropoiesis 1.
Pathophysiology of Iron in CKD Anemia
The anemia of CKD is fundamentally a hypoproliferative anemia with preserved iron stores 2. Here's why:
- EPO deficiency is the primary driver: The failing kidney cannot produce adequate erythropoietin, which is essential for salvaging early red blood cell progenitors (CFU-Es) from programmed cell death 2
- Iron remains sequestered: Without sufficient EPO signaling, erythropoiesis collapses at the early stages, so iron that would normally be incorporated into hemoglobin remains stored in bone marrow macrophages 1
- Abundant iron stores despite anemia: Research demonstrates that CKD mice develop "a hypoproliferative anemia" with "abundant iron stores in the bone marrow" despite severe anemia 1
The Critical Distinction: Absolute vs. Functional Iron Deficiency
However, this picture becomes more complex in real-world CKD patients:
Absolute iron deficiency (truly depleted stores) can coexist with CKD due to:
- Chronic blood losses (frequent phlebotomy, GI bleeding, dialysis-related losses)
- Impaired intestinal iron absorption 3
Functional iron deficiency develops when:
- Iron stores are adequate or high, but inflammation-driven hepcidin elevation blocks iron release from macrophages 4
- This prevents stored iron from reaching developing erythroblasts, creating a "kinetic" iron deficiency despite normal or elevated ferritin 4
Clinical Implications
In pure EPO-deficiency anemia (without complicating factors):
- Bone marrow examination would show normal to increased iron stores (hemosiderin-laden macrophages)
- Serum ferritin is typically normal or elevated
- The problem is utilization, not availability
Common pitfall: Many CKD patients have mixed pathology—both EPO deficiency AND true or functional iron deficiency 4, 5. The KDIGO guidelines emphasize that "anemia and iron deficiency are prevalent in patients with chronic kidney disease" 4, meaning these conditions frequently coexist rather than existing in isolation.
Diagnostic Approach
When evaluating a CKD patient with anemia:
- Serum ferritin >100 ng/mL (non-dialysis) or >200 ng/mL (hemodialysis) with TSAT >20% suggests adequate iron stores 4
- Lower values indicate absolute iron deficiency requiring iron supplementation before or alongside EPO therapy
- Bone marrow biopsy (rarely performed clinically) would show iron-laden macrophages in pure EPO-deficiency anemia 6
The key concept: EPO deficiency causes underutilization of available iron, not iron depletion, resulting in normal or increased bone marrow iron stores in uncomplicated cases 1.