title: Renal acidification defects in patients with recurrent calcium nephrolithiasis.
abstract: The frequency of renal tubular acidosis was evaluated in 28 adult patients with recurrent calcium nephrolithiasis (19 with 'renal' hypercalciuria, 9 with normocalciuria and no metabolic abnormality) and no evidence of obstruction or infection of the urinary tract. Eight patients with hypercalciuria (42%) had a defective renal reabsorption of bicarbonate, based on a fractional excretion of bicarbonate higher than 7% and a TmHCO3/GFR lower than 2.2 mEq/dl; 2 of them had an associated distal defect of acidification, as judged by a U-B pCO2 lower than 18 mm Hg in maximally alkaline urine. One patient with hypercalciuria had distal tubular acidosis, based on a urine pH higher than 5.3 during acidosis. Only 1 patient with normocalciuria had associated proximal and distal acidification defects. The remaining 8 patients displayed a normal renal acidifying capacity. The bicarbonate wastage was independent of serum PTH levels, vitamin D status and hypercalciuria and was associated with a defective tubular reabsorption of phosphate, increased random urinary pH and more active nephrolithiasis, with a prevalence of mixed calcium oxalate and phosphate stones. Our study shows a high incidence of defective tubular reabsorption of bicarbonate in patients with calcium nephrolithiasis and 'renal' hypercalciuria and suggests that the proximal acidification defect plays a pathogenetic role in promoting calcium nephrolithiasis.
mesh_terms: D000141:Acidosis, Renal Tubular / Q000209:etiology* / Q000503:physiopathology; D000328:Adult; D000643:Ammonium Chloride; D001639:Bicarbonates / Q000097:blood / Q000378:metabolism; D001769:Blood; D002118:Calcium / Q000378:metabolism* / Q000652:urine; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007669:Kidney Calculi / Q000150:complications* / Q000503:physiopathology; D007684:Kidney Tubules / Q000378:metabolism; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood; D010710:Phosphates / Q000378:metabolism; D014556:Urine
chemical_list: D001639:Bicarbonates; D010281:Parathyroid Hormone; D010710:Phosphates; D000643:Ammonium Chloride; D002118:Calcium