PTH and Marchiafava-Bignami disease: According to the CKD–MBD guidelines (Ketteler et al., 2017; GBD Chronic Kidney Disease Collaboration, 2020), the levels of Ca, Pi, and i-PTH in serum should be monitored in adult patients at the beginning of stage 3 CKD, and then the severity of CKD–MBD should be assessed based on the level of i-PTH.