title: Methods for diagnosing the risk factors of stone formation.
abstract: OBJECTIVE
  To compare various systems for assessing the risk of recurrent stones, based on the composition of urine.
  
  
  METHODS
  The relative supersaturation (RSS) of urine, the Tiselius Indices, the Robertson Risk Factor Algorithms (RRFA) and the BONN-Risk Index were compared in terms of the numbers of variables required to be measured, the ease of use of the system and the value of the information obtained.
  
  
  RESULTS
  The RSS methods require up to 14 analyses in every urine sample but measure the RSS of all the main constituents of kidney stones. The Tiselius Indices and the RRFA require only seven analyses. The Tiselius Indices yield information on the crystallisation potentials (CP) of calcium oxalate and calcium phosphate; the RRFA also provide information on the CP of uric acid. Both methods provide details on the particular urinary abnormalities that lead to the abnormal CP of that urine. The BONN-Risk Index requires two measurements in each urine sample but only provides information on the CP of calcium oxalate. Additional measurements in urine have to be made to identify the cause of any abnormality.
  
  
  CONCLUSIONS
  The methods that are based on measuring RSS are work-intensive and unsuitable for the routine screening of patients. The Tiselius Indices and the RRFA are equally good at predicting the risk of a patient forming further stones. The BONN-Risk Index provides no additional information about the causative factors for any abnormality detected.
authors.affiliation: Department of Physiology (Centre for Nephrology), The London Centre for Kidney Stone Research, Royal Free and University College London Medical School, London, UK.
authors.forename: William G
authors.initials: WG
authors.lastname: Robertson
keywords: BONN-Risk Index; CP, crystallisation potential; CaOx, calcium oxalate; CaP, calcium phosphate; Kidney stone; MAP, magnesium ammonium phosphate; NAE, net acid excretion; PRAL, potential renal acid load; PSF, overall biochemical risk of forming stones; RRFA, Robertson Risk Factor Algorithms; RSS, relative supersaturation; Relative supersaturation; Robertson Risk Factor Algorithms; Tiselius Indices; UA, uric acid