Calculator

Urinary Supersaturation Calculator

Calculates supersaturation ratios for the common stone types from twelve measured urine values, with the validated EQUIL2 algorithm, to assess kidney stone risk.

Results

Supersaturation results

Supersaturation ratio (SS) is the ratio of the actual product of ion activities to the solubility product: above 1 precipitation may occur, below 1 dissolution may occur, values near 1 indicate equilibrium. Negative delta Gibbs (ΔG) is the thermodynamic driving force for crystallization, in kcal/mol; positive values indicate a stronger tendency for crystal formation and higher risk.

Risk assessment

Calcium oxalate

Calcium phosphate (brushite)

Uric acid

Calcium : citrate ratio

This ratio assesses stone formation risk independently of supersaturation calculations: below 0.25 is low, 0.25–0.33 borderline and 0.33 or above high (Srivastava et al., Pediatr Res 2009).

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                            R code
                            Reproduces these results with the equil2 package.
                          

                          

                            
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                      About
                      
About EQUIL2

                      
This application calculates the saturation of ionic substances in urine from twelve measured values, following the EQUIL2 program of Werness and colleagues. It is intended for research use only.

                    

                    

                      

                        Inputs
                        
Sodium, potassium, calcium, magnesium, ammonium, chloride, phosphate, sulfate, oxalate, citrate, urate and pH.

                      

                      

                        Unit systems
                        
mmol/L (SI) or the mg/dL units of the original EQUIL2 program as published by Werness et al. Values are converted automatically when you switch; the core math and algorithm remain unchanged either way.

                      

                      

                        Reference
                        
Werness PG, Brown CM, Smith LH, Finlayson B. EQUIL2: A Basic Computer Program for the Calculation of Urinary Saturation. J Urol. 1985;134(6):1242-1244. doi:10.1016/s0022-5347(17)47703-2

                      

                    

                    

                      

                        Unit conversions
                        Applied when SI values are passed to the EQUIL2 engine
                      

                      

                        

                          Sodium
                          mmol/L (same in both systems)
                        

                        

                          Potassium
                          mmol/L (same in both systems)
                        

                        

                          Calcium
                          mmol/L → mg/dL
                        

                        

                          Magnesium
                          mmol/L → mg/dL
                        

                        

                          Ammonia
                          mmol/L → ug/dL
                        

                        

                          Chloride
                          mmol/L (same in both systems)
                        

                        

                          Phosphate
                          mmol/L → mg/dL of phosphorus (P), as labs report it
                        

                        

                          Sulfate
                          mmol/L → mEq/L
                        

                        

                          Oxalate
                          µmol/L → mg/L
                        

                        

                          Citrate
                          mmol/L → mg/L
                        

                        

                          Urate
                          mmol/L → mg/dL
                        

                      

                    

                    

                      When using the Original EQUIL2 Units option, values are passed directly to the algorithm without conversion. 
                      The code is translated from the EQUIL2 Visual Basic program; the R package is available on GitHub: 
                      github.com/billdenney/equil2
                      .