Martinez MG, dos Santos Silva V, do Valle AP, de Oliveira RC, Banin VB, Hokama NK, Martin LC: Association between Sodium Intake and Urinary Fractional Albumin and Immunoglobulin G Excretion in Chronic Nondialytic Renal Disease: A Prospective Longitudinal Study. Nephron DOI 10.1159/000500548
It is generally agreed that the magnitude and composition of proteins excreted in the urine has an important impact on the prognosis of chronic kidney disease (CKD). The influence of concomitant intake and excretion of salt (NaCl) on proteinuria has been incompletely characterized.
A prospective, observational study by Martinez and co-workers addresses this knowledge gap, at least in part. Eighty-four patients with CKD stages 1–4 exhibiting proteinuria of at least 500mg/d were examined at baseline and after 6 months (on stable management and dosing of renin-angiotensin system [RAS] inhibitors). Most (2/3rds) of the patients had diabetes mellitus, hypertensive nephrosclerosis or ischemic kidney disease. Urine albumin and IgG, creatinine and sodium (Na+) excretion were assessed and fractional excretion (FE) of albumin and IgG were calculated. Two groups of approximately equal size were compared: 1) Those with an increase in Na+ excretion over the period of observation (from 139mEq/d to 198mEq/d); 2) Those with a decrease in Na+ excretion over the period of observation (from 196mEq/d to 140mEq/d). The change in FE albumin correlated positively with the change in urinary Na+ excretion (r2= 0.294; p<0.001) as did FE IgG (r2=0.314; p<0.001). Systolic blood pressure also showed a positive correlation with variation in Na+ excretion, but dietary protein intake and glycemia did not.
These findings suggest that intake of NaCl has a material impact on parameter of urine protein excretion. Whether this effect is mediated by changes in systemic arterial pressure or intra-renal hemodynamic or something else (such as micro-inflammation cannot be conclusively analyzed in a study of this design. However, from a practical standpoint it emphasizes that NaCl intake needs to be considered in the interpretation of changes in urinary protein excretion over time in many patients with proteinuric CKD. But additional studies in patients with glomerulonephritis are needed to confirm the findings.
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