Evaluation of iron status in patients of chronic kidney disease - A study to assess the best indicators including serum transferrin receptor assay

Anemia is an early complication of chronic kidney disease (CKD). The iron deficiency is an important contributor, more so in the Indian population. As routine standalone iron tests do not accurately reflect the actual status in the complex environment of CKD, there is a need to study better indicators. Serum iron, ferritin, total iron-binding capacity (TIBC), and serum transferrin receptor (sTfR) levels were estimated in 100 primary iron deficiency anemia (IDA) patients (controls-Group 1) and 68 newly diagnosed CKD cases. The CKD patients were divided into two groups: Serum ferritin <=100 μg/L (Group 2) and >100 μg/L (Group 3). The values of percentage saturation, log of ferritin (log_ferritin), and the ratio of sTfR to log ferritin (sTfR/log_f or sTfR index) were calculated. The CKD cases were further divided depending on ferritin cut-offs of 30, 50, 70, and 100 μg/L and statistically analyzed including ROC and AUC, to choose the best diagnostic parameter for accurate assessment of iron status in CKD cases. The mean serum ferritin was 11.34 μg/L, 28.70 μg/L, and 281.81 μg/L, and the mean sTfR was 2.34 μg/ml, 1.82 μg/ml, and 1.28 μg/ml in Groups 1, 2, and 3. Among all groups, the difference was found to be significant for serum iron, log_ferritin, and sTfR/log_f. The sTfR and sTfR/log_f showed good discrimination between IDA and Anemia of chronic disease in CKD cases, but sTfR/log_f gave the best discrimination at all cut-off levels of ferritin. At a ferritin cut-off of 50 μg/L, the sTfR/log_f value of 0.83 had a sensitivity of 93.5% and specificity of 95.45%, and at a ferritin cut-off 100 μg/L, the same value of 0.83 had a sensitivity of 95.5% and specificity of 86.5%. The ratio of sTfR/log_f is the best indicator for assessing iron status in CKD.