Renal clearance of endogenous erythropoietin in patients with proteinuria

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Abstract
Recent data indicated the importance of urinary losses of erythropoietin (Epo) in the pathogenesis of anaemia in patients with nephrotic syndrome. In the present study we aimed to investigate plasma and urinary Epo levels and their renal handling in relation to β2-microglobulin (β2m), sodium metabolism and the renin-angiotensin-aldosterone system (RAAS), respectively, in patients with sub-nephrotic range proteinuria (SNP), microalbuminuric diabetics and hypertensives, and in healthy subjects studied on a standardized diet containing 120 mmol sodium and 70 g protein per day. We found that patients with SNP were characterized by lower plasma levels of Epo than healthy subjects but no differences were found in urinary excretion of Epo, endogenous Epo clearance and its fractional excretion (FEEpo). There were no differences between groups in FEβ2m and FENa and plasma aldoterone levels but plasma renin activity was higher in patients with SNP than in the controls. No relationships were found between Epo levels and activity of the RAAS and sodium metabolism, respectively. Our data suggest that lower levels of plasma Epo in patients with SNP and normal renal excretory function are not due to urinary losses of Epo but rather to the decreased production/degradation ratio.