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Abstract

We thank Dr Tang and colleagues for their constructive comments on our work [1Ascione R. Lloyd C.T. Underwood M.J. Gomes W.J. Angelini G.D. On-pump versus off-pump coronary revascularisation evaluation of renal function.Ann Thorac Surg. 1999; 68: 493-498Abstract Full Text Full Text PDF PubMed Scopus (366) Google Scholar]. Our study was intended to examine the influence of cardiopulmonary bypass and off-pump techniques on both glomerular and tubular renal function.N-acetyle glucosaminidase (NAG) is present in high activity in the tubular lysosomes; thus, its presence in the urine is a direct sign of tubular damage consisting of structural cellular changes. NAG release in the urine is not affected by dysfunction of other organs [2Price R.G. Measurement of N-acetyl-β-glucosaminidase and its isoenzymes in urine. Methods and clinical applications.Eur J Clin Chem Clin Biochem. 1992; 30: 693-705PubMed Google Scholar]. On the contrary, the retinol binding protein (RBP) is produced by the liver, released in the blood, filtered by the glomerulae, and reabsorbed with a saturable process by the proximal tubules. As such, the amount of RBP in the urine is an indirect sign of tubular dysfunction and may also represent glomeral dysfunction and liver injury. We would therefore urge potential investigators who wish to use RBP not to forget to carefully investigate the preoperative liver function and glomerular filtration, because this may alter the assessment of renal function. The lack of control of preoperative liver and glomerular function was indeed one of the main limitations of the study of Bernard and associates [3Bernard A.M. Vyskocil A.A. Mahieu P. Lauwerys R.R. Assessment of urinary retinol-binding protein as an index of proximal tubular injury.Clin Chem. 1987; 33: 775-779PubMed Google Scholar] and Tang and associates [4Tang A.T.M. El-Gamel A. Keevil B. Yonan N. Deiraniya A.K. The effect of ‘renal-dose’ dopamine on renal tubular function following cardiac surgery assessed by measuring retinol binding protein (RBP).Eur J Cardiothoracic Surg. 1999; 15: 717-722Crossref PubMed Scopus (85) Google Scholar].With regard to the use of nephrotoxic agents that may have affected renal tubular function, we can confirm that none of the patients in the study received nonsteroid, antiinflammatory drugs, and a low dose of dopamine was required in 6 and 3 patients in the on- and off-pump groups, respectively, in the postoperative period, in accordance with our intensive care unit protocol to improve hemodynamic conditions. We thank Dr Tang and colleagues for their constructive comments on our work [1Ascione R. Lloyd C.T. Underwood M.J. Gomes W.J. Angelini G.D. On-pump versus off-pump coronary revascularisation evaluation of renal function.Ann Thorac Surg. 1999; 68: 493-498Abstract Full Text Full Text PDF PubMed Scopus (366) Google Scholar]. Our study was intended to examine the influence of cardiopulmonary bypass and off-pump techniques on both glomerular and tubular renal function. N-acetyle glucosaminidase (NAG) is present in high activity in the tubular lysosomes; thus, its presence in the urine is a direct sign of tubular damage consisting of structural cellular changes. NAG release in the urine is not affected by dysfunction of other organs [2Price R.G. Measurement of N-acetyl-β-glucosaminidase and its isoenzymes in urine. Methods and clinical applications.Eur J Clin Chem Clin Biochem. 1992; 30: 693-705PubMed Google Scholar]. On the contrary, the retinol binding protein (RBP) is produced by the liver, released in the blood, filtered by the glomerulae, and reabsorbed with a saturable process by the proximal tubules. As such, the amount of RBP in the urine is an indirect sign of tubular dysfunction and may also represent glomeral dysfunction and liver injury. We would therefore urge potential investigators who wish to use RBP not to forget to carefully investigate the preoperative liver function and glomerular filtration, because this may alter the assessment of renal function. The lack of control of preoperative liver and glomerular function was indeed one of the main limitations of the study of Bernard and associates [3Bernard A.M. Vyskocil A.A. Mahieu P. Lauwerys R.R. Assessment of urinary retinol-binding protein as an index of proximal tubular injury.Clin Chem. 1987; 33: 775-779PubMed Google Scholar] and Tang and associates [4Tang A.T.M. El-Gamel A. Keevil B. Yonan N. Deiraniya A.K. The effect of ‘renal-dose’ dopamine on renal tubular function following cardiac surgery assessed by measuring retinol binding protein (RBP).Eur J Cardiothoracic Surg. 1999; 15: 717-722Crossref PubMed Scopus (85) Google Scholar]. With regard to the use of nephrotoxic agents that may have affected renal tubular function, we can confirm that none of the patients in the study received nonsteroid, antiinflammatory drugs, and a low dose of dopamine was required in 6 and 3 patients in the on- and off-pump groups, respectively, in the postoperative period, in accordance with our intensive care unit protocol to improve hemodynamic conditions.