Background and objectives: For addressing the influence of muscle mass on serum and urinary creatinine and serum cystatin C, body composition was assessed by skinfold thickness measurement and bioelectrical impedance analyses. Design, setting, participants, & measurements: A total of 170 healthy individuals (92 women, 78 men) were classified as sedentary or with mild or moderate/intense physical activity. Blood, 24-h urine samples, and 24-h food recall were obtained from all individuals. Results: Serum and urinary creatinine correlated significantly with body weight, but the level of correlation with lean mass was even greater. There was no significant correlation between body weight and lean mass with cystatin C. Individuals with moderate/intense physical activity presented significantly lower mean body mass index (23.1 ± 2.5 versus 25.7 ± 3.9 kg/m²) and higher lean mass (55.3 ± 10.0 versus 48.5 ± 10.4%), serum creatinine (1.04 ± 0.12 versus 0.95 ± 0.17 mg/dl), urinary creatinine (1437 ± 471 versus 1231 ± 430 mg/24 h), protein intake (1.4 ± 0.6 versus 1.1 ± 0.6 g/kg per d), and meat intake (0.7 ± 0.3 versus 0.5 ± 0.4 g/kg per d) than the sedentary individuals. Conversely, mean serum cystatin did not differ between these two groups. A multivariate analysis of covariance showed that lean mass was significantly related to serum and urinary creatinine but not with cystatin, even after adjustment for protein/meat intake and physical activity. Conclusions: Cystatin C may represent a more adequate alternative to assess renal function in individuals with higher muscle mass when mild kidney impairment is suspected.

Bartter syndrome is an inherited renal tubular disorder caused by a defective salt reabsorption in the thick ascending limb of loop of Henle, resulting in salt wasting, hypokalemia, and metabolic alkalosis. Mutations of several genes encoding the transporters and channels involved in salt reabsorption in the thick ascending limb cause different types of Bartter syndrome. A poor phenotype–genotype relationship due to the interaction with other cotransporters and different degrees of compensation through alternative pathways is currently reported. However, phenotypic identification still remains the first step to guide the suspicion of Bartter syndrome. Given the rarity of the syndrome, and the lack of genetic characterization in most cases, limited clinical evidence for treatment is available and the therapy is based mainly on the comprehension of renal physiology and relies on the physician’s personal experiences. A better understanding of the mutated channels and transporters could possibly generate targets for specific treatment in the future, also encompassing drugs aiming to correct deficiencies in folding or plasma membrane expression of the mutated proteins.

Background and objectives: Nephrolithiasis (LIT) is more prevalent in patients with autosomal dominant polycystic kidney disease (ADPKD) than in the general population. Renal ultrasonography may underdetect renal stones because of difficulties imposed by parenchymal and/or cyst wall calcifications. Design, setting, participants, & measurements: A total of 125 patients with ADPKD underwent ultrasonography and unenhanced computed tomography (CT) scan, routine blood chemistry, and spot and 24-h urine collections. Results: CT scan detected calculi in 32 patients, including 20 whose previous ultrasonography revealed no calculi. The percentage of hypocitraturia was high but not statistically different between patients with ADPKD+LIT or ADPKD. Hyperuricosuria and distal renal tubular acidosis were less prevalent but also did not differ between groups, whereas hyperoxaluria was significantly higher in the former. Hypercalciuria was not detected. Renal volume was significantly higher in patients with ADPKD+LIT versus ADPKD, and a stepwise multivariate logistic regression analysis showed that a renal volume ≥500 ml was a significant predictor of LIT in patients with ADPKD and normal renal function, after adjustments for age and hypertension. Conclusions: CT scan was better than ultrasonography to detect LIT in patients with ADPKD. Larger kidneys from patients with ADPKD were more prone to develop stones, irrespective of the presence of metabolic disturbances.

Purpose of review Decreased bone mineral density and increased prevalence of bone fractures have been found in patients with idiopathic hypercalciuria. The purpose of this review is to summarize the recent published evidence that supports a potential role of the bone, and its link to the kidney and intestine, in the pathogenesis of idiopathic hypercalciuria. The effects of hypercalciuria on bone and the implications for treatment are also reviewed. Recent findings Evidence suggests that the incidence of a first fracture in kidney stone patients is fourfold higher than the control population. Support for the role of bone in the pathophysiology of hypercalciuria has been corroborated. New studies have detailed the effects of several cytokines – increased number and sensitivity of vitamin D receptors, and increased acid production – upon the bone acting cells. Similarly, recent clinical and experimental studies have suggested that genetic factors confer a predisposition to the formation of renal calcium stones and bone demineralization. Summary Whether hypercalciuria is the result of a primary bone disorder, a consequence of a persisting negative calcium balance or a combination of both still remains to be determined. Nevertheless, bone status must be evaluated and followed up in patients with idiopathic hypercalciuria.