Introduction: The production of erythrocytes is regulated by the hormone erythropoietin (EPO), which maintains the blood haemoglobin (Hb) levels. Human EPO is a glycoprotein hormone and its synthesis is controlled by the hypoxia-inducible transcription factor.
Panjeta M et al showed that in patients with native kidneys and CKD, GFR positively correlated with Hb and EPO levels, but there aren´t studies that have described this correlation in kidney transplant recipients.
Method: Observational, analytical, transversal and prospective study from January 2021 to February 2023. Were included all G5 KDIGO chronic kidney patients who completed 3 years post-transplant during the study period at Central Military Hospital, Mexico, City. All subjets were divided into 4 subgroups according to their GFR. Serum iron kinetics and erythropoietin levels were determined. Exclusion and elimination criteria were: subjects denied informed consent, those patients with digestive tract bleeding and subjects with erythropoietin use. The Kolmogorov-Smirnov test was performed to determine the normality of the variables, data was reported as median and interquartile range (IQR); descriptive and analytical statistics were performed with Xi², Kruskal Wallis test and ANOVA tests. p< 0.05 was statistically significant.
Results: Were included 114 kidney transplant recipients. On average, kidney grafts are functional, defined by a GFR ≥ 60 ml/min/1.73 m²BS. Whole parameters levels of iron kinetics are normal in our kidney transplant recipients including EPO levels.

There was a correlation trend but without statistical significance between Hb and serum EPO levels (p=0.051), but not between EPO levels and eGFR (p=0.28). Furthermore, we demonstrate an inverse correlation between the creatinine level and the EPO levels (p<0.001).

Discussion: Milkos ZN reported in 886 prevalent kidney transplant recipients the erythropoietin mean was 10.85 IU/L, similar to our results. In native kidneys, EPO deficiency begins early in the course of CKD, but when eGFR ≤ 30 ml/min/1.73 m²BS this deficiency increases.
By other side, Sinnamon KT et al found a significant negative correlation between hemoglobin levels and EPO (Pearson's correlation coefficient, R=-0.29, p< 0.001) but there was no significant correlation between EPO levels and eGFR (R=0.02, p=0.74) in kidney transplants, similar to our results.
Conclusion: In Mexican kidney transplant recipients, the EPO level doesn´t correlate with eGFR. This implies that graft function isn´t the main determinant of serum EPO levels in renal transplant recipients and other factors such as hypoxia-inducible factor (HIF) and hepcidin levels should be analyzed in future prospective studies.