A recent publication has suggested that low and high serum magnesium are important prognostic factors in feline CKD. Plasma total magnesium concentrations are relatively stable in cats with IRIS stage 2 and 3 CKD and become elevated when renal excretory function is severely impaired in IRIS stage 4 CKD. Jonathan Elliott at RVC and Henk van den Broek at Utrecht University look at their recent study involving 174 cats with azotemic CKD, identifying hypomagnesemia (defined as serum total magnesium concentration <0.71 mmol/l) in 9%, 18% and 10% of cats with IRIS stage 2, 3, and 4 CKD, respectively.