Clinical utility of serum soluble transferrin receptor levels and comparison with bone marrow iron stores as an index for iron-deficient erythropoiesis in a heterogeneous group of patients

Aim: To evaluate the correlation between raised soluble transferrin receptor (sTfR) and stainable marrow iron, and to define the utility of sTfR in discriminating between the presence or absence of iron-deficient erythropoiesis in patients with anaemia of chronic disease. Methods: Seventy-six consecutive adult patients without accelerated erythropoiesis who had undergone bone marrow (BM) aspiration/trephine for various clinical reasons during 2003-2006 were studied. All patients had serum iron studies (iron, transferrin and ferritin) and sTfR performed within 1 week of BM aspiration/trephine. These 76 patients were assigned to three groups based on the iron status of the BM and sTfR level: patients with normal sTfR and normal BM iron stores (n=49), patients with an elevated sTfR and normal BM iron stores (n=13) and patients reduced or absent BM iron stores (n=14). Means (95% confidence interval) for mean corpuscular volume (MCV), mean corpuscular haemoglobin concentration (MCHC), red blood cell haemoglobin (RBC Hb) content and median (5(th) and 95(th) percentiles) for haemoglobin were then calculated. Results: All patients with absent BM iron stores had an elevated sTfR level. Patients with normal BM iron stores and elevated sTfR levels had significantly lower Hb, MCV, MCHC and RBC Hb content than patients with normal BM iron stores and normal sTfR levels. Conclusion: sTfR is the most sensitive serum biochemical marker for the identification of iron-deficient erythropoiesis. Normal BM iron stores can coexist with elevated sTfR and decreased MCV and MCHC. sTfR levels correlate better than BM iron stores with decreased MCV and MCHC. Therefore, sTfR is a useful marker of iron-deficient erythropoiesis, due to both absent iron stores, and restricted iron supply due to anaemia of chronic disease. As a single investigation, however, sTfR does not discriminate between these two causes of iron-deficient erythropoiesis.