Zhou H, Yang M, Jiang Z, Ding J, Di J, Cui L: Renal Hypoxia: An Important Prognostic Marker in Patients with Chronic Kidney Disease. Am J Nephrol 2018;48:46–55
An adaptation of magnetic resonance imaging (MRI) technology has made it possible to non-invasively asses the state of blood oxygenation in renal tissue (tissue deoxyhemoglobin concentration or R2*), also called BOLD-MRI.
Zhou and colleagues studied 60 patients with various forms of CKD (mostly diabetes-related and glomerulonephritis) by BOLD-MRI in a prospective observational design. Both cortical (CR2*) and medullary (MR2*) oxygenation levels were assessed separately. A Kaplan-Meier analysis showed that the lowest CR2* levels (better oxygenation, lower deoxyhemoglobin) predicted a favorable outcome determined by an end-point of a 30 % or more decline in GFRe from baseline GFR or ESRD, after a median follow-up of 3.2 years. The association of high CR2* (poorer oxygenation) with unfavorable outcomes persisted after adjustment for possible confounding variables (age, gender, diabetes, proteinuria, but not therapy). The level of CR2*, but not that of MR2*, were reasonably reproducible. The study did not examine whether interventions designed to enhance tissue oxygenation improved outcomes, so these findings are primarily correlative and not causal in nature. This study is largely confirmatory of other studies . Nevertheless, this is a promising new beginning for an old avenue of research highlighting a possible important role of tissue hypoxia in progression of CKD. Whether high deoxygenation of renal cortical tissue is modifiable biomarker of CKD progression must await further studies. An adaptive increase in oxygen consumption of hypertrophied residual nephrons in the face of constant or decreasing supply of oxygen is a distinct possible explanation for these findings.
1. Pruijm M et al., Reduced cortical oxygenation predicts a progressive decline of renal function in patients with chronic kidney disease. Kidney Int. 2018 Apr;93(4):932-940