Erythrocyte and reticulocyte indices in iron deficiency in chronic kidney disease: comparison of two methods

OBJECTIVE: Anaemia is a common complication of chronic kidney disease (CKD), particularly in dialysis patients. The recent European guidelines for anaemia treatment in CKD indicate the percentage of hypochromic red cells (%HYPO) and reticulocyte haemoglobin content (CHr) calculated by Siemens ADVIA haematology analysers as a useful tool indicating iron deficiency. The aim of this study was to evaluate the agreement between CHr and %HYPO parameters and the reticulocyte haemoglobin equivalent (RET-He) and red blood cell haemoglobin equivalent (RBC-He) calculated by the Sysmex XE-2100 haematology analyser in a cohort of 200 dialysis patients referred to the Nephrology Unit of our hospital. Furthermore, we evaluated a new index, the DF-Hypo XE, obtained from haemoglobin (Hb), haematocrit (Hct) and RET-He, provided by the Sysmex XE-2100, as a new potential marker of %HYPO in dialysed patients. MATERIAL AND METHODS: Blood samples collected in EDTA anticoagulant from 200 CKD patients receiving erythropoietin and iron to maintain haemoglobin level between 10 and 12 mg/dL were analysed on both the Siemens ADVIA 2120 and the Sysmex XE-2100 within 2 h of collection. RESULTS: There was good correlation between CHr and RET-He (r = 0.88; p<0.0001), %HYPO and DF-Hypo XE (r = 0.89; p<0.0001) and between RBC-He and CH (r = 0.96; p<0.0001), but there was a lower correlation, even though statistically significant, between RBC-He and %HYPO (r = -0.59; p<0.0001). The Altman-Bland analysis showed a very good level of agreement between CHr and RET-He (mean bias = 1.04 pg), %HYPO and DF-Hypo XE (mean bias = 1.73). Using a cut-off value of 29.4 pg for the RET-He and of 10.2 for the DF-Hypo XE, 15 out 17 patients with a CHr <29.0 pg and 9 out 11 patients with a %Hypo <10.0% were respectively correctly identified. CONCLUSIONS: Our study shows good correlation and agreement between CHr and RET-He and between %HYPO and DF-Hypo XE in evaluating CKD patients needing iron support.