Serum ferritin <70 μg/L predicts functional iron deficiency in patients with chronic kidney disease

Anemia is a common complication of chronic kidney disease (CKD) which is treated by erythropoiesis-stimulating agents. However, most of the patients do not respond adequately due to the development of functional iron deficiency (FID). The study was conducted to explore the value of inflammatory markers, high sensitivity C-reactive protein (hsCRP) and interleukin-6 (IL-6) along with serum ferritin (SF) in the diagnosis of FID. Seventy-seven clinically diagnosed patients of CKD (Stage 3, 4, and 5) of either sex, age >18 years with hemoglobin <11 g/dL were included in the study. Complete hemogram with peripheral smear, serum iron, total iron binding capacity, transferrin saturation, SF, transferrin receptors (sTfR), hsCRP, IL-6, and erythrocyte sedimentation rate were estimated and statistically analyzed. sTfR/log ferritin (taken as gold standard) detected 31/77 patients as having iron-deficient erythropoiesis. Nineteen patients were detected as having FID. SF at a cut-off <70 μg/L showed the best sensitivity (83.87%) and specificity (73.91%) in detecting FID in these patients and identified 14/19 cases of FID. The 5 FID cases who were missed had raised hsCRP. The presence of raised hsCRP reduced the sensitivity to 79.16%. SF <70 μg/L emerged as the most sensitive and specific in the identification of iron-deficient erythropoiesis. SF >12 μg/L - SF <70 μg/L was able to identify 14/19 cases of FID. Furthermore, hsCRP further stratified the subgroup of CKD patients in which FID could be detected with higher sensitivity and specificity.