Influence of albumin infusion on the urinary excretion of beta(2)-microglobulin in patients with proteinuria

Branten, AJW Wetzels, JFM

Ajw. Branten et Jfm. Wetzels, Influence of albumin infusion on the urinary excretion of beta(2)-microglobulin in patients with proteinuria, NEPHRON, 81(3), 1999, pp. 329-333

18

INGLESE

Article

Urology & Nephrology","da verificare

NEPHRON

0028-2766 → ACNP

81

3

1999

329 - 333

ISI

0028-2766(199903)81:3<329:IOAIOT>2.0.ZU;2-P

Most filtered proteins are reabsorbed by the renal proximal tubule by a mec hanism that involves binding to the brush border membrane and endocytosis. Under normal conditions the low-molecular-weight protein beta(2)-microglobu lin (beta(2)M) which is used to detect tubular injury, is reabsorbed almost completely. However, in proteinuric patients an increased urinary excretio n of beta(2)M may not simply reflect tubular damage but might also result f rom a decreased tubular reabsorption due to competitive mechanisms. To exam ine the magnitude of such an effect we have studied the renal effects of al bumin infusion (40 g in 2 h of a 20% solution) in 10 patients with a glomer ular disease and proteinuria >3.5 g/24 h. Before, during and after albumin infusion the GFR (inulin clearance), RPF (PAH clearance), blood pressure an d the urinary excretion of albumin, IgG, transferrin and beta(2)M were meas ured. Albumin infusion resulted in a slight decrease of the GFR (72 +/- 11 ml/min before and 67 +/- 10 ml/min after infusion), an increase of the RPF (379 +/- 66 ml/min before and 445 +/- 83 ml/min after), a decrease of the f iltration fraction (0.20 before and 0.17 after), and hemodilution. After in fusion the urinary excretion of albumin increased from 4.5 +/- 0.7 to 8.4 /- 1.6 mg/min (p < 0.05). The urinary excretion of IgG and transferrin incr eased, probably reflecting a change in glomerular size-selectivity. In cont rast, the urinary excretion of beta(2)M did not change significantly (basel ine 12 +/- 5 mu g/min, end 13 +/- 6 mu g/min, percentage change 16.8 +/- 11 %). To correct for changes in tubular load we calculated the fractional rea bsorption of beta(2)M The initial rise in albuminuria during infusion did n ot affect fractional tubular reabsorption (Delta%: 0.72 +/- 0.52%, median 0 .005%). In the period after infusion a slight decrease was noted (median -0 .33%, p < 0.01). A decrease in the fractional reabsorption was particularly observed in patients with pre-existing tubular damage. In conclusion: infu sion of albumin in proteinuric patients has no clinically relevant effect o n the tubular reabsorption of beta(2)M. Therefore, beta(2)M is useful as a parameter to detect tubular injury and alterations in tubular handling of p roteins in patients with proteinuria and glomerular diseases.