Correlation of renal oxygenation with renal function in chronic kidney disease: a preliminary prospective study

Introduction: Chronic hypoxia is prevalent in chronic kidney disease (CKD), and Blood oxygenation level-dependent magnetic resonance imaging (BOLD-MRI) provides noninvasive evaluation of renal oxygenation. This study aimed to explore the correlation of renal oxygenation evaluated by BOLD-MRI with renal function. Methods: 97 non-dialysis patients with CKD stages 1-5 and healthy volunteers (HVs) were recruited in the study. Based on their estimated glomerular filtration rate (eGFR), the patients were divided into two groups: CKD stages 1-3 (CKD 1-3) and CKD stages 4-5 (CKD 4-5) . We measured cortical and medullary T2* (COT2* and MET2*) values in all participants by BOLD-MRI. Physiological indices were also recorded and compared among three groups. Correlation of T2* values with clinical characteristics were determined. Results: The COT2* values were significantly higher than MET2* values in all participants. The COT2* and MET2* values of three groups were ranked as HV> CKD 1-3> CKD 4-5 (p< 0.0001). There were positive correlations between the COT2* values, MET2* values and eGFR, hemoglobin (r> 0.4, p< 0.01). The 24-h urinary protein (24-h Upr) shown weak correlation with the COT2* value (rs= -0.2301, p= 0.0265), and no correlation with the MET2* value (p> 0.05). Urinary microprotein, including urinary alpha1-microglobulin (alpha 1-MG), urinary beta2-microglobulin (beta 2-MG), and urinary retinol binding protein (RBP), was showed strong correlation with COT2* and MET2* values. According to analysis of receiver-operating characteristic (ROC) curve, we obtained the optimal cut-point between HV and CKD 1-3 were "< 61.17 ms" (sensitivity: 91.23%, specificity: 100%) for COT2* values and "< 35.00 ms" (sensitivity: 77.19%, specificity: 100%) for MET2* values, whereas COT2* values ("< 47.34 ms"; sensitivity: 90.00%, specificity: 92.98%) and MET2* values ("< 25.09 ms"; sensitivity: 97.50%, specificity: 80.70%) between CKD 1-3 and CKD 4-5. Conclusion: The decline of renal oxygenation reflected on T2* values, especially in cortex, may be an effective diagnostic-marker for early detection of CKD.