Measurement of glomerular filtration rate by the 99mTc-DTPA renogram is less precise than measured and predicted creatinine clearance.

The work was devised to compare measurements of glomerular filtration rate (GFR) by technetium-99m-diethylenetriaminepentacetic acid (99mTc-DTPA) renogram to those by creatinine clearance (measured and predicted by Cockroft and Gault) and by inulin clearance. A total number of 65 individuals were enrolled: 15 healthy controls and 50 patients with renal disease. Compared to inulin clearance used as the gold standard, 99mTc-DTPA overestimated at low and underestimated at high GFRs. 99mTc-DTPA measurements were less precise than creatinine clearance except for individuals with GFR >100 ml/min x 1.73 m2. Measured creatinine clearance had the highest correlation coefficient with inulin clearance, 99mTc-DTPA clearance the lowest. In correlation analyses, 81.5% of the interindividual variability for measured creatinine clearance could be explained by true differences in inulin clearance; this value dropped to 59.1 and 57.4% for predicted creatinine clearance and 99mTc-DTPA, respectively. In patients with GFR <25 ml/min x 1.73 m2, all 99mTc-DTPA measurements were out of the 95% confidence interval for the inulin measurement. It can be inferred that 99mTc-DTPA clearance from the renogram is less precise than measured and predicted creatinine clearance.

The renal hemodynamic response to an oral protein load is normal in IgA nephropathy.

The study was devised to explore the effects of an acute oral protein load on renal hemodynamic response in patients with IgA nephropathy (IgAN). The study was performed in 10 proteinuric IgAN patients (800 +/- 300 mg/day) and in 20 healthy controls (matched by sex, age, BMI, BSA, plasma creatinine, plasma urea, urinary urea and protein intake). Blood pressure and creatinine clearance were nearly identical in the two groups. GFR and RPF, measured as the clearance of inulin and of p-aminohippurate (PAH) were studied before and after a meat meal which provided 2 g of protein/kg BW. Following the protein load, renal reserve, percent renal reserve and postmeal cumulative changes of GFR were not significantly different in IgAN and controls. Filtration fraction (FF) at baseline was significantly higher (p < 0.01) in IgAN than in controls (25.5 +/- 1.41 vs. 19 +/- 2%). Postmeal hyperemia and hyperfiltration did not affect FF in either group. Filtration capacity in IgAN was lower (p<0.02) than in controls (117 +/- 5.6 vs. 137.9 +/- 7.0 ml/min x 1.73 m2), whereas the percent of filtration capacity utilized at rest was identical in controls and in IgAN. Creatinine clearance overestimated GFR in IgAN. The data indicate that renal hemodynamic response to proteins in IgAN is normal.

Update on renal acidification: a physiological view.

The kidney plays a major role in the regulation of acid-base balance. This process is mainly dependent on H+ secretion in the tubular lumen. Two acid extruder proteins are involved: the Na+/H+ exchanger and H(+)-ATPase. Studies using in vivo and in vitro microperfusion and isolated membrane vesicles have clearly demonstrated that the Na+/H+ exchanger is the main mechanism regulating H+ secretion/HCO3- reabsorption along the proximal nephron. Moreover, several reports indicate that this protein is involved in intracellular pH (pHi) regulation. Newer studies using molecular biology techniques have identified at least five isoforms of the Na+/H+ exchanger: NHE-1 is the housekeeping isoform, while NHE-3 seems to be implicated in transepithelial acid-base transport, although other isoforms could be involved too. H(+)-ATPase is the major acid extruder protein along the distal nephron, but it is also expressed along the proximal tubule, where a Na(+)-independent bicarbonate reabsorption has been described. There are a few studies indicating that the proton pump participates in pHi regulation, particularly in the presence of a large acid load. Its absence along the distal nephron may be one of the causes of distal tubular acidosis.

Renal reserve is normal in adults born with unilateral renal agenesis and is not related to hyperfiltration or renal failure.

This study was carried out to examine the renal hemodynamic response in adult patients with single kidneys born with unilateral renal agenesis. A group of 21 patients with unilateral renal agenesis were divided into three groups according to their glomerular filtration rate (GFR): 112 +/- 3 ml/min x 1.73 m2 in group A, 68 +/- 3.2 ml/min x 1.73 m2 in group B, and 40.7 +/- 3.3 ml/min x 1.73 m2 in group C. Mean arterial blood pressure was significantly higher in the patients of group C who were also proteinuric. The renal hemodynamic response to an oral protein load (2 g/kg of protein as beefsteak) was normal in all groups and unrelated to hyperfiltration or to renal failure and proteinuria. The study indicates that in patients with renal agenesis, the hemodynamic response to a protein challenge is similar to that of kidney donors, renal transplant recipients and uninephrectomized patients. The paper also demonstrates that the renal response to a protein challenge is inadequate to identify patients with renal agenesis who are at risk of developing renal disease. Finally, in renal agenesis with renal disease, creatinine clearance overestimated the GFR by an average of 32.7%.