Proteinuria and Everolimus. The Relevance of Knowing Urinary Sodium Excretion in a Kidney Transplant Patient

A sixty-four year old male with a seven-year history of kidney transplantation started with increasing amounts of proteinuria. His maintenance immunosuppression consisted on meprednisone 4 mg/day, sodium mycophenolate 720 mg/day and everolimus 1.5 mg/day for the last three years. Two years after being on this regime, he started to display increasing amounts of proteinuria and no hematuria, while his kidney function remained steady and his blood pressure was normal. A Doppler sonogram was normal; anti- HLA antibodies were negative and a kidney biopsy revealed mild mesangial expansion and 15% of interstitial fibrosis and tubular atrophy; C4d stain was negative. Twenty four urinary sodium was 385mEq/day. He was started on a 3 g sodium/day diet. Two months later urinary sodium excretion dropped to77 mEq/day and proteinuria decreased from a maximum of 3.85 g/day to 0.7 g/day. At first glance, the initial approach to reduce proteinuria would have been to withdraw everolimus, as it is a well-known cause of proteinuria. This case report underscores the relevance sodium tubular reabsorption plays on proteinuria and on glomerular filtration, showing that urinary ionograms are mandatory when the assessment of proteinuria is undertaken. It also calls the attention of nephrologists to pursue proteinuria and to treat it accordingly in the transplant population, as it is a cardiovascular risk factor and a surrogate of chronic kidney disease and of kidney disease progression.