title: Calcium phosphate stone morphology can reliably predict distal renal tubular acidosis.
abstract: OBJECTIVE
  Calcium stones represent 85% to 90% of all urinary calculi, including various crystalline compositions and etiological conditions. Calcium phosphate accounts for 10% to 15% of cases. These stones are mainly related to 3 groups of risk factors, including calcium or phosphate metabolism disturbance, renal acidification defects and urinary tract infection. Identifying the stone etiology often requires extensive metabolic evaluation. We assessed whether stone analysis including morphological typing in addition to stone composition could be a valuable help for diagnosis.
  
  
  METHODS
  Of 60,564 stones analyzed by morphological examination and infrared spectroscopy at our laboratory 6,439 (10.6%) were mainly composed of carbapatite. Of these stone 1,093 patients were included in study who had an available etiological diagnosis and stones containing at least 70% of calcium phosphate without struvite.
  
  
  RESULTS
  Of the 1,093 calcium phosphate stones 12.8% showed a peculiar morphology termed IVa2, characterized by a smooth aspect and a glazed brown-yellow appearance with tiny cracks. IVa2 morphology was observed in 96.1% of stones associated with inherited distal renal tubular acidosis. In contrast, the other stones of similar composition but different morphology were related to distal renal tubular acidosis in only 3.9% of cases. In addition, IVa2 stones were found in 65% of calcium phosphate stone formers associated with Sjögren syndrome and in 35% of calcium phosphate stones in patients with medullary sponge kidney. These 2 conditions are related to a mild to moderate distal acidification defect.
  
  
  CONCLUSIONS
  Identifying IVa2 stone morphology is clinically relevant because it should prompt clinicians to search for complete or incomplete distal acidosis and initiate specific therapy to decrease recurrence.
authors.affiliation: Centre National de la Recherche, Laboratoire de Physique des Solides, Université Paris-11, Orsay, France; Institut National de la Santé et de la Recherche Médicale, Unités Mixtes de Recherche 1138, Centre de Recherche des Cordeliers, Laboratoire de Physiopathologie Orale Moléculaire, Equipe Berdal, Université Paris-5, Université Paris-6, Université Paris-7, Paris, France. Electronic address: arnaud.dessombz@crc.jussieu.fr.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Dessombz
authors.affiliation: Sorbonne Universités, Université Pierre et Marie Curie Paris-6, Paris, France; Assistance Publique-Hôpitaux de Paris, Service des Explorations Fonctionnelles and Institut National de la Santé et de la Recherche Médicale, Unités Mixtes de Recherche S 1155, Hôpital Tenon, Paris, France.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Letavernier
authors.affiliation: Sorbonne Universités, Université Pierre et Marie Curie Paris-6, Paris, France; Assistance Publique-Hôpitaux de Paris, Service des Explorations Fonctionnelles and Institut National de la Santé et de la Recherche Médicale, Unités Mixtes de Recherche S 1155, Hôpital Tenon, Paris, France.
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Haymann
authors.affiliation: Centre National de la Recherche Scientique, Laboratoire de Chimie de la Matière Condensée de Paris, Université Pierre et Marie Curie Paris-6, Collège de France, Paris, France.
authors.forename: Dominique
authors.initials: D
authors.lastname: Bazin
authors.affiliation: Assistance Publique-Hôpitaux de Paris, Service des Explorations Fonctionnelles and Institut National de la Santé et de la Recherche Médicale, Unités Mixtes de Recherche S 1155, Hôpital Tenon, Paris, France.
authors.forename: Michel
authors.initials: M
authors.lastname: Daudon
mesh_terms: D000141:Acidosis, Renal Tubular / Q000175:diagnosis* / Q000209:etiology; D002130:Calcium Phosphates / Q000032:analysis*; D006801:Humans; D007669:Kidney Calculi / Q000737:chemistry* / Q000150:complications / Q000473:pathology*; D011237:Predictive Value of Tests; D015203:Reproducibility of Results
chemical_list: D002130:Calcium Phosphates; C020243:calcium phosphate
keywords: acidosis; calcium phosphate; diagnosis; kidney; nephrolithiasis; renal tubular